I recently decided to get back into the game. I first played in 2002-2003 when Infinity Challenge was released. I started to do some research and most of it has been confusing at best. So I came here to see if anyone who currently or recently played can give me and tips on where to start to get back into it?

With so many sets out I also wonder can heroes from different sets be mixed or would I have to play with an all marvel(example) set?
I prefer Marvel and would like to build a set with them first. But any help is appreciated.