UE is a game engine that can be used to make games with ease with their blueprints that help with coding issues and for template projects with helpful tips! Some use it to make actual games, and some (like me!) use it to make mods for some games!
Well that really depends on the game, usually if it has EAC, then yes, it's bannable because of the ways of getting around it's blocking, but sometimes it isn't! Sadly, the games I do mod are bannable but I'm not too stressed about it so... yea; my opinion is that if the other person cannot see it, it matches the original model you're replacing and if it doesn't provide any ingame advantage (hell sometimes it could make a big disadvantage for the person using it), then I think it should be okay, but no one cares about that.
...No? I have actually gotten asked this before and it's really confusing, sometimes people will say "Illegal" to refer to the games rules/tos/eac tos/whatever the fuck, so uhmmmm no not in laws.
No actually I'm quite alright, you can find out on your own.
It really depends on what it is, I've modded plently of Nintendo games, where SSBU was my first introduction to making mods and using... the gross tooblox kit... the ui makes it really annoying and difficult, so I don't mod much Nintendo games anymore, I focus more on UE games based on the fact that it's something I can do really fast if I really wanted to.
Here's some of my work done on UE games!