I’m short on time so I’ll just jot down some quick answers.
You don’t need a degree. As long as you have a strong portfolio, nobody will even look for any of that.
Photoshop, Slate and a 3d package like Houdini or Maya. Most effect work is done in engine/editor.
Pick one you like the look of. If you want to do Overwatch stuff, I’d go for unreal. If you want to do mobile games, go for unity.
I knew basic mel when I got my first job and I learned the rest along the way, but it’s not needed. There are plenty of vfx artists who don’t script at all.
Start by checking out tutorials. ImbueFX has some good ones on Youtube. I’m working as fast as I can on a course as well. Keep reading this forum, there are a few how to get started posts with good info.
How to judge, well, compare yourself to the effects in the game you want to work on. Are you close? Apply!