I hope giving your notice went well! It sounds like you are doing the right thing based on your situation. A bad boss can really wreak havoc with your self esteem. It feels awful now, but in a month or two you'll wonder why you put up with it for as long as you did

I don't think you need to tell your boss why you are leaving. If it comes to it, just say it's a bad fit or some other vague thing. It will be much easier to get a good reference if you leave as pleasantly as possible-- and why add more stress to the situation by confronting your boss?

I would not give more than a two week notice. I did the last time because I felt guilty about quitting. It was a mistake. It meant four weeks of abuse and hostility as opposed to two weeks.

Congrats on your new future! It is a hard step to take, but once you get it over with, you will feel so good!