Welcome to Gaia! ::

Well, you would have to work out all the bugs, and it would be best to start with this system in place. Would probably be easier to just do normal type role play.

Here is a system I came up with for someone else, as we where talking. Can't remember the persons name though...

Oh well, here is what I have for a system I was planing of using.

As for a game system, have abilities and attacks cause only so much damage and you assign HP polls for everyone? Have them level up, and gain EX points for killing NPCs and monsters? Also, hitting should be a dice system, probably a d-10 system. You roll the dice and it determines if you hit, and if you do, how much damage you cause.
ex: I attack! (Roll 10 sided dice (d10))
I got a 5. I hit, but only cause half damage.
or... I got a 10! A crit! I cause double damage! Yes!
or....... I got a 1! NOOO! I miss, attacking a friend/myself doing half damage to him/her! Sorry! crying

You would have to work out stuff, give everyone an HP pool and MP pool as well as determine how much damage characters do at what levels. Maybe even have a new class system. Mage, fighter, engineer as a few ideas. Mage would have low damage, but good magic pools and damaging spells. Spells always hit, so you roll for damage. (Reason they would always hit is that they cost you MP, unto which you only have a limited amount of.)
Engineer (or whatever you have for another class) would cause low damage, have some magic abilities, but would have some other abilities that would help support other characters, like encouragements, repair, healing or something. This class could be anything really. I just threw in engineer as an example.

For that to work, you would need to have everything worked out very well, and explained as well. It would all have to be written down for people.