[Silent Wizard]

2)I know at level 20 you can class change. What I was wondering, is if I don't do the class change until later on for whatever reason, like level 22 or 25, will I lose anything like stat gains? Should I do it right at level 20 for max benefit?

The class change is not like you can change from a cleric to an archer for instance. It is a job title change and must be completed before you can equip any lev 20+ gear.