Edit: rewrote the post, was a bit too messy and unclear on a number of different issues, added a few things too. Also was written a little hastily.
This combo/setup has some major problems, firstly there's very little in the way of AOE damage which will be needed (as you zig-zag have pointed out). No matter what your hero abilities are AOE is lacking and needed.
Second: TimeM Mage (TM) concentrating on the offence is probably not the best idea as then you forget about him and he dies. Also it depends weather or not your in Tournament Rules or not. If you are then you've got only your own SB and nothing else (which would make it a little more difficult for you to offend).
Continuing with the TM his ulti (ultimate) cannot keep you alive indefinitely. There will be times where you just can't do anything. Also it can be very easy for Time Stop to be triggered, some offence at the right time will do it. Best times could be Just before Spiders or either Stunner Wave. Simply put you get stunned/netted and you will be killed very quickly. Even BC's Innate cannot save you here as it's easily dispelled. Once there are a number of creeps present then there will be too much to do and you will die. Can't be helped.
marx:
Troll, about him tanking a ranged wave, are you nuts? why should he be tanking??? He is not a tank, not at all. There's no reason to get him a Bloodstone ring. Yes it improves his str (health / damage) but there is no reason for it)
There are 4 places on the map (preferable places on each side of the map) where the troll can sit and kill everything. He sits on either of the ledges above or below the combo/wood shop, to the ledge near the armor/boots shop or at the bottom of the base (these are the ledges that I'm talking about).
The best thing one can get for the troll is more speed (TM's job) but he will need a little more damage. It's his Behead that needs to proc so a bloodstone ring won't be of much use.
The biggest issue for the troll is Bloodboil. While it is a great ability you would need a steady stream of creeps for it to work properly with vamp pots (especially when it's on a high level, lets say greater then level6). One could easily die from the ability (I've seen it quite often). Also vamp pots have a large cd so you can't spam the ability or risk the chance of a quick death.
MI:
For the MI getting Ironbarks can't and won't happen for ages even with ppl pooling as there are other needs. To get by without ironbarks there's telo boots (winged leather boots) for the stun, TM's speed for cripple and AM pots. Why bother getting Ironbarks soooooo early when there are better work arounds for the early game.
Another big problem with the Infuser is that his abilities take up mana. One aspect / situation which you have not addressed. Since you are probably (more like definitely) increasing his attack speed his lvl1 n lvl6 (can't remember their names) will proc more often. Therefore taking up more mana then usual. So, with that, he will be left with virtually no mana for his ultimate. Also it is the case that he will be more then likely surrounded it will be very difficult if not impossible to get him a mana pot. He might be able to use his ulti once but not a second time if needed (which I think will be the case).
Forgot to add the MI's lvl 6 ability which is great doesn't really work for anyone else. It has a short duration (<3 secs I think) so therefore no one else will really get a hit in.
BC:
Probably the strongest link in here. His innate (Chorus of mad men I think is the name) helps to no end. Failure of the Forge and slow are another 2 great abilities that the whole team will benefit from. Also his ulti, say no more.
Equipment:
As I said Ironbarks are not the best thing to get sooo early, also there's no point in going on about armor, it's a given. Also there is no need for a bloodstone ring. What would be better is the small All stats ring. It only adds +12 to everything but his attack speed, mana regen and health will benefit from it. The mana regen will allow the infuser to use his ulti twice then once, which also means that you can probably get him a mana pot much more easily. After that the large all stats ring and then maybe ironbarks followed by thirsting blade (but it could be more worth while getting the BT before the ironbarks). You need him to survive long enough for his ulti the 2 rings will do that better then just getting ironbarks.
For the troll he definitely needs telo boots, best item for him. If he has to come off his purch (that is if you have him sitting upon the ledges) the the combo boots are good to have. It is debatable weather or not to get him some "heavy hitter" (thinking nimsha and spineripper). It is preferable but not always necessary since his lvl1 Behead should take down most creeps in about 2 hits. If you have a heavy hitter with him then I would go for the nimsha first (I'll explain why later on) and later on spineripper.
For the TM you only need hisans and nothing else (maybe the odd mana pot and possible the Eldar Staff for the mana regen). Also for the BC you won't need much. Pots, armor n telo boots. Anything else is just a waste on either hero.
Play Style:
Since you've got the MI as the main tank and the troll as the damage dealer (as I understand), I would suggest not to group in the middle. The troll can tank until the spiders on his own without any issues. After the wolves have gone the troll runs back to the center and ports to the safe area. There he can kill everything and if one or two pass by, no worries. They will more then likely have low hp's. Here he can stay for the game and come down only when needed or offensed against.
For the MI and BC: both will be attacking creeps for the first few waves until possibly the MI has the small all stats ring. The the BC backs off and is played like a caster. No longer will he go into combat, the only time he may have to is if the MI dies. TM is the runner and will get everything for everyone.
Also why get a nimsha for the troll? Well since he can tank...well more likely kill a single lane he would be on his own. Since he is on one ledge the BC would be on the other. The best way of keeping yourself alive is back into a corner where you've got as few creeps as possible (talking about the MI here). Here the BC is standing himself upon the ledge drawing no creeps. His Failure is really helping the MI here. The MI can kill much more quickly.
If both the MI and the BC were in the middle with the troll sitting upon the ledge the troll would be getting agro (not so bad) but then it happens that a number of creeps are coming after him and he can't handle them all. Also the MI would be surrounded by so many creeps that he runs the risk of dying or if he's about to, the TM Time Stops (can have it's pros n cons but it could prove costly later). Here both of your tanks can easily die / be killed. Also since the BC is close by the MI he will also be drawing agro away from the MI, Greater chance of him dying since he has no real equipment.
For increasing his hammer (stun proc) I would suggest not going about lvl2 until you reach lvl 22/24. Yes it's a great ability and the chance for it to happen will increase......but......with it proc'ing so much your mana will be drained very quickly, espically with the TM's speed ability. Level up everything else then level it up and you should be fine at that stage. It is also a big con of this setup too. Finally when applying ability points at lvl 8 and 14 don't add any. Leave your hero as is. I know it's tempting but if you leave it for lvl's 9 n 15 you can get both combat and his lvl6 on both occasions (or his ulti and one other at lvl15).
Offending:
MI is one of the easiest to offend. Stun + Ahrat (or Uthmor) = Death (usually). With the troll Drunkness + Effegy and he's dead. There's a big chance that the Image/Clone (for lack of a better term) will have already killed him and is currently running down to kill either the Tm or BC (or both) before you dispell or if you have and the offender is doing it correctly he has either waited until after the dispell or have moved him away.
Another Spell is the plague where you loose 3% of your hp/s (can't remember the name of it). Chances are that your pot CD won't have happened quickly enough, result....Death.
Offending on a TM is a waste of time unless he's a nuub or an idiot (which can happen), or if his reactions are slow (can happen).
Cons:
As Zig-zag stated there's a lack of AOE. This is the biggest drawback of this combo. And that could hurt you later on when you need some clearance.
The TM is the weakest link here as far as I'm concerned. His ulti (Time Stop) can be a great help and Savior but it is also the biggest pit fall of this team build. Time Stop at the wrong time or creep wave and you will be smashed. No amount of MI's ulit could help and the troll would be just too consumed with creeps that they simple run over you.
Suggestions:
My first suggestion would be for the TM to be swapped for Hypno. Hypno's prediction one the MI will save you sooooo much cash. No need for any rings saving you somewhere between 40-220k which can be used on other items (ironbarks being your fave
). But also his innate Moonbeam (MB) can help the MI to no end for him mana hungry ways. No more mana pots. If it so happens that the MI is in trouble and standing near or under his MB Mind Shout. Then if you are lvl 10 port in n ulti it. Recast MB and give the MI his pots n gear, finally walk out killing everything (or a lot anyway). That's you AOE sorted. Hypno will be of a greater asset to you then the TM.
You also could swap the MI for Grake or Paladin (but that too brings up more issues with creep agro). The Troll could be swapped for a caster, Ice Mistress for instance. There are a number of changes that one could make but I personally would stick with Hypno instead of TM.
Well that's it. Sorry if the previous version was illegible was being a bit too quick in writing it. Dam just after reading that and went into waaaaaaaayyyyy tooooooooo much detail, have fun
). But also his innate Moonbeam (MB) can help the MI to no end for him mana hungry ways. No more mana pots. If it so happens that the MI is in trouble and standing near or under his MB Mind Shout. Then if you are lvl 10 port in n ulti it. Recast MB and give the MI his pots n gear, finally walk out killing everything (or a lot anyway). That's you AOE sorted. Hypno will be of a greater asset to you then the TM. 
