Tire wise check out the tire forum - tons of info there. 265/75R16 BFG AT/KOs should fit nicely (that's what I have).

Do a search for bilstein and you'll find the part numbers you need for new shocks (bils are the best bet for an Xterra).

On the t-bars, just make sure you can still slide your index finger between the UCA and the bump-stop - if you go any higher you'll start to get a bouncy ride from hitting the bumpstops frequently.