Cloud obviously comes back after the poisoning from the mako energy, but when? Also, after getting the first huge materia, were do u go?

try goin back to cloud and talk to him... then starts the slow process of getting him back... tho it is a bit trippy.... :p

*POSSIBLE SPOILERS*

Yeah, the first huge materia was that one in Fort Condor (you should've picked up Phoenix summon from there) Go to North Corel's mako reactor and you'll fight some dudes and then get on the train. I do suggest saving your game before heading to the reactor because you miss out on Barret's final limit break and a free Ultima materia if you stuff it up because the train crashes into North Corel (lol) So yeah, get it right. Then after you've got that go back to Mideel and stuff will happen.

Actually, you can do it in either order, so it's possible ad may have already done North Corel. If so, do the minigame in Fort Condor to get the other materia. I love this minigame, it's my favorite in the game. However, if you are going into Corel, remember when you get to the final part where you're controlling the train: If your other characters complain that you're going too fast, just keep doing what you're doing. That's just to sike you out, but once they say that you're going too fast, just keep doing what you're doing and you should be okay. Basically it's just one of those wacky "keep alternating the controls as fast as you can" thing.