There are four classes in total - Halfling Wizard, Elven Rogue, Human Fighter and Dwarven Cleric. You'll need a total of 700,000 experience to get to level 10 and this is equal to about 1.5 playthroughs of the game, including all side quests.
On Chapter two you go out the right door, kill every mob until the arena (that place where the relic has to get to 100%) kill everything in there then come back the way you came (mobs respawned. You gets Health pots at arena too, loads. It's about 5-7 exp bars a run depending on level, and time is normally 15 minutes but the levels will vary. Also, it is best to do it on single player because mobs die so much quicker.