What level of torment do the legendaries and set items begin to drop a decent amount?
Can a wizard solo this level? If so, with what build?

Set items I believe only drop t1+ but legs drop from norm - t10.
A wizard can solo norm through t10 if obviously geared, so if you're not, I recommend you test some builds and put a big fat red gem in your weapon for more damage.

EDIT: Oh and if you're not geared, I would suggest you run with blizzard snowbound and hydra arcane.

This post was edited by dsphantom on Sep 28 2015 05:59am

but what would be some higher tier gear for the wizard so that it could solo t7?

yes

Tal rasha, firebird and opus set (although im not one hunna about its capabilities in t6+)

all you need to know

http://www.icy-veins.com/d3/wizard-vyr-archon-lightning-patch-2-3