We chose 4x4 when purchasing our TV and it has come in handy at least a few times each year while towing our TT. We prefer boondocking and have been in spots where without 4x4 capabilities we wouldn't have been able to get into, and more importantly get out of these secluded sites.
If you don't plan to go offroad much with your TT a 4x2 would be just fine. Would be less expensive, less components to worry about, and more towing capacity since adding 4x4 will reduce it by how much these added components weigh. MPG reduction with 4x4 is very minimal but it does still exist to a degree.
Today's half-tons are more than capable for your current TT GVWR, but going with a 3/4 ton will allow you to go with a larger TT later down the road. If you plan to go to a larger 5er in the future a 1 ton would be a better choice since pin weight is much heavier than tongue weight.
Ultimately, it's your choice as only you know how you plan to use your rig, and since you are already thinking of a larger rig in the future a bigger TV might be a better starting point. Whatever you decide, here's hoping you have many great times and wonderful memories using your new TT and truck.