Money

How important is it to invest money into LOL? Because I am thinking about doing so

Lol is a game where you don't have to spend any money to be better than your opponent.

Okay, actually there are some skins that give you visual advantages, like some of the lux that you don't see as skills, so you can't avoid it.

Don't do that.
The game is getting boring, and it's not pay to win...