bevinator: If you play as a thief, it's entirely possible to max out your stats. Thieves level up faster than fighters or mages, and with all of the free stat bonuses from quests and the like, you can get everything up to 25 even without lots of tattoos. Technically you can do this with any type of character, but it's easier with thieves due to the levelling. The max level of PST is actually 99, though you're more likely to be 20-30 by the end of the game, unless you farm lots of monsters for XP.
And you CAN farm monsters for xp... LOTS of them. Curst, Undersigil, and the Modron Maze are the best for that. However, it's kinda pointless honestly. You'll likely be more than powerful enough by the end of the game even without grinding. Even my magey characters tend to be able to stab monsters to death with ease. Late-game Undersigil has Greater Glabrezus, though, which can drop some REALLY nice items. (Heaven and Earth, Bell's Shield, Umei Kaihen, Ring Zero)
I like killing everything that moves, just for fun. :)