I'm sure plenty of folk will be better placed than me on that front.
Any recommendations on spells to buy?
I have very few points invested in magic so far. I ended up on sneak, smithing, enchanting. The rest are for pickpocket (to get 100extra carry weight) and for upping light armour, one handed & bow damage.
I tend to rely on destruction to maybe adept level spells. The rest are levelled through use mostly.
Regularly used spells for me are transmute (for earning cash potential), fast healing, candlelight for finding chests and loot in the dark, flames, fireballs, lightning etc for combat.
There is a nice staff from a daedric quest I use instead of conjuration, but a follower usually helps about as much.
I have found some handy shouts too so use them more in fights. My Breton has a magic resistant power which is rather useful so you may want a spell for that.