I don't have specific formula's, sadly, but I will try to give a good explanation on how it works.
Basically damage works like this: Weapon Damage+item modifier damage(rings, amulets, ammo if applicable)+Skills damage modifiers=Your damage. This is further increased with skills.
Defense is your armor+skills modifier. Defense does not add up with each peice, there instead is area-specific damage. Each part of the body has a certain chance of getting hit. You will notice that shields are near the defense of a warrior chest peice, the thing is the shield gaurds the entire body. So you effectively nearly double your defense, or more than double it, with a shield. Also shields block. Certain attacks may have different chances for hitting different body parts, i'm not sure.
Your damage output is BASICALLY(but not actually) your damage-enemies defense for body part hit. This applies for all weapons.
Hit chance is calculated by your accuracy by the enemies evasian. I haven't been able to test this, sorry.
All weapons(YES, Force[Magic] and launchers too!) have a chance to do critical damage and a chance to miss. They all work the same.
The critical damage isn't constant for all weapons. Diffirent weapons have different base critical rates and different critical hit damages. I haven't been able to test exactly how this works.
CCR did mages right in this game. They aren't so ungodly overpowered and make warriors useless because they ignore armor and sheilds and whatever else liek they do in other games. Other games make what in my opinion is a mistake by not making mages abide by normal damage formula's that balance out the other classes. Staves are required to cast force(except for dark/holy) and staves have damage like any other weapon. The difference is that mages will constantly cast spells, spending FP to chaincast nonstop. The only normal attack is a weak staff hit that does low damage, you will never use that. The timers of force skills allow you to cast them constantly.
All weapons, including staves, launchers, throwing knives, ETC are ubgradable with talics(search for more info) and intense drops of them can be found. The only weapons you can't upgrade with talics or find intense of are summons and mechs(which is why mechs are bad later on).