I just ascended my first character (yeah, I've been playing a while, but I've been exploring and didn't do any runs) and I have question about changing the second class.

I have all the quests logged up and ready to go, but can you do them all and then decide what class to pick? and can I do 1, change, go get skills throughout the game come back and change again?

sorry for such a newbieish question, but I'm rather confused on the whole thing and I've been told a few different answers so I figured I'd head here and ask the experts.

Thanks in advance for your help.