Great Basin, you are well-prepared for bicycle touring with your backpacking experience. Your backpacking gear will be great for bicycle touring. I went the opposite direction, from bicycle touring to backpacking. I quickly spent a lot of money getting lighter and more compact gear. My backpacking gear does take up four paniers on the bike. One pannier is dedicated to the "kitchen", my stove and food. I do strive to have the top of my rear rack empty for use on the road. Extra water and a compact chair may end up there.
Your selection of the Surly LHT is excellent. The used bike market is fickle. You can score a great deal or search a long time for the right bike in the right size. My current touring bike is an expensive folder. But I still have my "normal" touring bike. It is a Nishiki from the 1980s. It was a 12-speed that I upgraded to a triple crank. I like to be able to pedal my load up the steep hills. I bought the bike used for $30.