In theory, you can play your character any way you want and combine any skills you want to build your character. But in some games, splitting your focus between too many unrelated skills just leads to a subpar character (e.g. you may be level 10 but because of your mix of skills, you struggle a lot with lvl 10 enemies).
So, if I level up a little bit of everything, will I have issues dealing with enemies later in the game?