Answer 1

Any kind of code but you have to save with what precise exention .txt .py .java .js ....

Answer 2

you can write any codes on notepad. (just save with the proper extension) The whole point of notepad++ and other IDEs is to package a lot of good features in one place. Like syntax issue highlighting, code color differences, and some have a local terminal to run your code on.
notepad does not.

Answer 3

You're on the right track! Just take em one at a time. You'll see and hear it a million times but get a good grasp on html, move onto css, accept that you can't learn ALL of css, then learn javascript for starters. And there's no time frame, you'll know when you're comfortable