Now, I would say, put one point in each school. The way that you can increase your chances to have lots of points for your spells would be to use the "Hall of Secrets" and the other vendor (I for his name) that allows you to trade 1 Talent point for 10 skill points. Take only the Talents that you need (which should not be too many with a mage) and trade the rest for skill points. I can not tell how the endgame will be with a non-lone wolf mage, but with my (LW) mage, I have 2 schools at 5, 2 schools at 4 and 1 at level 3. My defenses are good (at least 3 in each) and I have both blacksmith & crafting at 5. Lore master is at 4 (trying to find some good to get it to 5) My resistances are over 100%, which is great because I can use the fire spells and sit in them, while the enemies take damage. My character is level 18 and I think I am almost done with the game...
It would be wise to have like an idea or a sheet with the spells you want and which level you can use them.
For the planning, you can use my guide, which gives a good detailed look into every skill and which level you get them.
You can find it here:
SKILL GUIDE I hope the information I provided you helps.
