Just bought a TT and don't have a TV for it yet. One friend, who tows a lot of heavy things, recommends nothing less than 3/4 ton P/U. A mechanic friend, who we will be camping with, says his 1/2 to...
4wd adds a bit of weight and this weight may even reduce the tow rating accordingly. As for handling, you can't run conventional 4WD on dry pavement, so it can't help your handling. All wheel drive (full time 4WD) can help with handling when one hits somewhat slippery surfaces (icy patches, for example), but I know of no pickups with AWD offhand.
4WD will be handy when you have to move your trailer on slippery inclines at low speeds, stuff like that.