So I know that once you have 20 con, you start to regenerate hps. However, is this only for warrior classes? Or if, say, my dwarf thief has 20 con, will he regenerate as well?
I'm not positive, but I am pretty certain it is for any character regardless of class. You could always try using console commands or a save editor to run a quick test. Either way, though, the health regeneration is quite slow and really, it is not worth putting that much on a support character like a mage or thief.
CON regen works for all characters and classes 20 CON: 1hp/6 rounds 21 CON: 1hp/5 rounds 22 CON: 1hp/4 rounds 23 CON: 1hp/3 rounds 24 CON: 1hp/2 rounds 25 CON: 1hp/1 round