You need 25 or 50 points, I believe. Then you'll have an edit button on your profile page near your default picture to change it.
You earn badges and milestones for that, yeah, but most of your reputation will come from people liking, agreeing with, laughing at, or finding your posts insightful.
I remember seeing a page somewhere with all recent discussions instead of just categories a while ago and it was the best thing ever, but I haven't been able to find it. I think it was on mobile, you know how different it is from the main site after all.
It is on mobile and I wish it was available for the main version as well.
Wonderful, more trash. The same trash that I have in 3 other event skins now.
I like it the way it is. If anything, I'd appreciate some darker tones and maps but it seems like we'll be getting that in Castle so I'm all set. I never care about graphics at all. Performance and framerate will always be more important to me.