Some question before I start

Hi I want to buy the game but I wanted to know some thing before I start and couldn't find the answer on google

If you have a seal equiped but you're not actively using it, can you still use incantations?

Is there a way to track walking museliums?

Can you equip more than 1 great rune at once? I

Can change my class or am I locked in this style for the full Playthough

Any help isreallyc Apriciated