also (without any major spoilers please) what chapter will i finally get to pick a 3 person team as so far a team of 3 has been very rare but when i have had a trio battles always seemed that little bit more fun and with 2 they seem to be a bit drawn out.
Chapter 11. You can change and adapt your team then.
Can you reset the Crystarium?
Also - are any of the characters best suited to certain roles./combinations?
No, afaik you can't reset it, but if need be you can always farm some more CP and end up stronger overall. You're going to have to buy every upgrade eventually anyway. The only ones that might not be worth it are the "techniques", as they can only be used by the party leader, so there's no point unlocking them if you never use that character as the leader. Also, later on, try to prioritize certain upgrades over others. Abilities should come before stats, and take note of CP cost. A +20 strength upgrade costing 8000 is better than a +16 strength upgrade costing 10000.
For the stage 8 crystarium, it is best to only go round the middle circle (and any abilities that branch off) first. This is because the stat bonuses that branch off the circle are more expensive, often for lesser stat boosts.
As for specific roles, not really. Most of the characters can do Ravager roles, with the exception of Fang (ravagers aren't really for the main damage anyway, I find). The roles I typically use characters for are:
Lightning - Commando (high strength = high damage)
Sazh - Synergist (he has haste, very important later on)
Hope - Medic (high magic)
Vanille - Medic (not as high magic as Hope, but more medic abilities - also gets a weapon with boosted cure ability)
Fang - Saboteur (slow is useful)
Snow - Sentinel (high HP)
I'm actually training Fang's ravager role up at the moment, as that is the only reason I don't use her. Her sentinel and saboteur roles are excellent (as well as commando for when the chain gauge is high), but I like my Tri-disaster/Relentless Assault paradigm. Also, when I level Lightning's Synergist role up to use haste, I can swap Sazh out, and use my ideal team of Lightning, Fang and Vanille.
I don't want to start again!)
