You are allowed to take three skills in character creation only, no matter how many skill schools you pick. Choose wisely, but don't worry too much, as you'll be able to pick up fresh skills soon after reaching town.
There are more low-level skills you can learn immediately than you are allowed to choose from in character creation. Most skills have to be purchased from a vendor to learn, although there are some pre-placed skillbooks lying around in certain places.
Generally speaking, you should only focus on two main skill schools, as there are not enough points in the game to max out more than three abilities (and trying to max out a third ability will eat up essentially eat up all your points). Taking more than two schools is possible, but only if you don't plan to go too far into some of the trees.
Rank 4 in a spell school allows you one master spell. Since there is only one "powerful" spell in each spell school, it makes sense to get rank 4 in each of the elemental schools. That gives you access to all 4 of the once-per-combat ultimate, Meteor shower, Hail attack, Earthquake, and Storm. There are more than enough points to do this. in fact, you could even reach rank 4 in all 5 spell schools if you wanted.
