I'm playing a pure mage character. I have a couple of questions for the experts out there:

Is there any kind of penalty wearing heavy armor as a mage?

Is there some benefit to wearing robes (which is an all-in-one torso, legs, & head piece) versus standard light armor (which includes separate torso piece, legs piece, and head piece). Seems like you would have a much stronger set of armor by using standard light armor and enchanting each piece separately versus enchanting just a single robe. Am I missing something?

When your enchant skill is low robes are better. Later though you should enchant a armor of your choice.

You get no penalties for wearing HA as a mage.

Light is good if you melee a bit and summon atronachs to help out. It's got a good perk for stam regen, which you won't be putting many points in. Cloth if you're going to be an enchanter. Heavy if you melee a bit and don't have a tank.

Some of the buff spells are more effective when not wearing armor. That's the only effect that I've noticed. If you're already wearing armor, then you won't need them anyway.

Robes only count as a torso piece as well - you can wear gloves, boots, and hood alongside robes, all with their own enchant slots. There are 2 main benefits for a mage wearing robes:

1) You get access to the powerful enchantments present on many of them, e.g. Adept Robes of Destruction giving you -17% Destruction cost and +100% Magicka regen.This enchant can't be duplicated to the same magnitude until you get the lv100 enchanting perk.

2) The Mage Armor perk makes Alteration armor spells more effective if you're not wearing any armor pieces. Even some Fur Bracers will prevent this perk from working.