Honestly, I kind of hate the storm atronach. Bulky, clumsy and those shock spells are too limited. I prefer the dremora lord--fast, aggressive and does damage with both the blade and the blade's fire enchantment. One caveat: if your follower accidentally hits the dremora with a spell or arrow it will attack your follower, and you have to either let them duke it out between themselves or kill one of them off yourself.
I use restoration, conjuration, alternation & illusion spells a lot so I go for the perks in those, but only for the level of spells I actually use (like for illusion, I rarely use spells over apprentice) and prefer to use enchantments that add magicka rather than cut the cost of specific spells. I don't apply level up points unevenly--that has always ended with me getting stuck in a bad position one way or another, so now I apply level up points evenly, no matter what.
Once you get to a high enough level, you can find enchanted circlets that add 70 magicka points, on top of any other add magicka enchantments you use. That way you can have plenty of magicka to use spells from any of the schools. Or at least that's how I prefer to do it.
By the way, to be able to conjure a Expert level creature before you have the magicka or skill level to do so, go find Sam Guevenne at one of the taverns after you're reached level 14 or so. He appears at a random tavern that you've already visited at least once once you hit the perquisite level. He'll be the dude in the black robe who asks you if you want to have a drinking contest. This will star the Daedric quest A Night to Remember. Once you complete that quest, you get Saguine Rose, a staff that conjures a dremora lord regardless of your level (although using staffs do not increase any skill level).
There are also Conjure Storm Atronach scrolls take you can use at any level, but they aren't common, either as loot or as items for sell.
