What armor or attire do spellcasters usually wear? I didn't think robes with just a destruction or conjuration perk would be enough to survive the mighty wilds, but I didn't think people would be decked out in all heavy armor either. Just a set of light?

Another: is the only real option for casters to trap souls the Soul Trap spell? 1h or 2h types can use the enchanted weapons killing 2 birds with one stone, but is a casters only real viable option to use Soul Trap? thanks

If you go join the Imperials, you get the option for "Medium Armour" which is a mix of both Heavy and Light according to the Blacksmith. But you actually have to join them, so if you were going for Stormcloaks, then no go. And as far as I know, there is no other Medium Armour in the game. Could be wrong though. Also, if you were going for a Battlemage sorta thing, use Robes, and then go with Heavy Armour on everything else (Boots, Helmet, Gloves...), not only is it effective for both taking damage and casting magic. But it also looks nice.

And about the soul trap, I would say if you really wanted souls without having to use the soul trap spell, you would have too get the enemy to really low health, then smack em with a soul trapped dagger.

Without getting too spoilery, if you finish the Mage College questline, you'll get two items of apparel that you'll wear for quite a while. If you level up enchanting a bit, though, you might find you're better off enchanting a set of light armor with the "XXX spells cost XX% less to cast" enchantments, although you'll have to level enchantment pretty high before you'll start to approach what compares with the other combo that I mentioned.

Also, there are staves with the Soul Trap spell. I personally find those much more convenient to use than the actual spell, because they don't use any precious magicka.

1: Armor for a pure maybe its robes/clothes and the alteration tree for armor skin spells.(I'd avoid perking the armor spells since the master spell does not use them) Summons help in that they take hits for you. It is better just to wear light or heavy armor and enchant it, it gives better protection and you don't have to spam a spell every minutes.

2. Soul trap can also be done via the conjuration bound weapon spells with a perk 2 or 3 into the tree. I think it has to be the killing blow though it does not seem to put a soul trap effect on the creature for X seconds. But I wracked up tons of souls through this with the bound bow.