Day Late & Dollar short (new to the game!)

So I recently discovered this game via the new Phoenix Unleashed release thank to Amazon's algorithm. Then I looked this up via reddit and saw an Onslaught character coming?! So clearly I have to collect these whether i play or not. The only miniatures game im familiar with is Heroclix but the ORIGINAL first release. Ive never painted before...So here's what I am doing:

1. Calling all of my local shops to support them by finding X-Men characters/villains (they're my favorite.)

2. Watching Youtube videos for how to play and painting tutorials.

3. What I can't find at my local small business, i'm purchasing online.

4. I plan to sit in at a local hobby shop for the MCP game night soon. They seem to be the only store with a player base. All of the other local shops dont carry the game anymore or host.

So here are my questions:

1. I am not a big fan of Avengers characters, but should I get the core set or can I wait for the X-Men starter set?
2. Sold out characters, are they coming back? The main website isn't that clear to me.
3. Should I wait for the affiliate packs for the re-release of figures that are confirmed, or just buy them now if I see them?
   1. Are their stats updated as well or just a re-release?
4. Terrain play mats and actual terrain pieces, can I hold off for now and use a grid play mat?
5. Any advice for a newb? Because it feels overwhelming trying to figure out what was released, what is sold out, what has been announced but not release details
6. And am I missing anything?

Thanks all!