notsofastmyboy: Spellcasters don't use mana or some other form of magical energy. They use spell slots you can "load" with the spells you want to use. The number and level of spell slots depends on the mage's or cleric's level. Also, mages gain bonus spell slots depending on the moon. In all honesty, the manual answers all your question about how magic works, so check it out. It's not much to read.

As for weapons, mages have a very, VERY limited selection; quarterstaff for melee, darts for ranged combat. You should definitely keep single-class mages out of melee combat. Also, mages will usually be a bit of dead weight at first, but that changes once they rise in levels.

Also, Magic Missile is a bit weak at first because the damage it does depends on the mage's level. A simple Sleep spell is often a lot more useful at early levels.