Leveling up

[Jurosementalistile]

Hi, I just have some general questions about leveling up and increasing your skills. Basically, does anyone know how the calculations are done? In particular I'm interested in magic, and in fact nature magic I suppose more than combat. I have been a combat wizard so far and my score is about 17, with my nature magic being about 2, and the same for the other two scores. But now I'm thinking maybe I'd like to be a nature wizard, or maybe even get both scores high. Is there any penalty for doing this? Does it take longer to take your scores up in one ability if your total level is higher? Do different spells raise your score at different speeds? Does attacking monsters with spells raise it faster than using non-combat spells, and does the monster involved make a difference?
Any helpful info would be appreciated, thanks.

[Ravager]

AFAIK, level affects what spells you can cast, but generally I try to split between two levels with most characters to get more versatility.