Some questions: How to get (re)started in the magical world of AOE 2

Hello! So the warning is that I'm really out of touch with video games, so bear with me please :D.

So I used to play AOC as a kid right after it came out with my friends with like 4 play LAN setup, and then a year ago while I should have been doing other things I realized that there was this Forgotten Empires expansion so I downloaded it and have been playing against the AI (which is harder than it used to be!).

Now I've been lurking this sub for a while and saw that HD is now a thing and see that it has a good online community going but I'm really clueless as to how to get this going. So my questions are:

1. To buy the game I have to download Steam and through Steam I buy it, that is the only way to do it?

2. To get started playing against other real people does it connect straight through the game itself? I don't know what Voobly, Twitch, all these things are but the main question is just to start playing against other people who aren't going to destroy me in my inexperience.

3. Is there anything significantly new in the HD I should know about? I saw there are more civs...

4. Any other advice you can think of for someone in my situation.

Thanks :)