Tires: I'd suggest something 32 to 37 mm wide. I like any of Schwalbe's touring tires, but there are many other suitable brands as well. I'd go with the Schwalbe Marathon Dupreme, size 622-37 (if you have 700 wheels).
Stem: Personal preference. Try the one you have first.
Saddle: The Brooks B-17 is probably the most commonly recommended saddle. But I'd first try the saddle you already have to see if it is good for you. If you get the B-17, make sure you get it 1000 miles in advance of your start.
Brakes: V-brakes are common for touring bikes, and I think the LHT does not have them.
Seat post suspension: just say no
Pedals: I'd go with SPD, simple and reliable.
Computer: Planet Bike Protege 9.0 (wired--eliminates possible interference problems with wireless). I'd skip the GPS as it uses too much battery power and you won't likely need it.
Front light: None. Don't plan to ride in the dark. If you get caught out unexpectedly, use your camp flashlight.
Rear light: Any bright red flashing thing. I like one that mounts to the rear of the rack so it isn't blocked by my gear. Planet Bike makes a rack-mounted light.
Pump: Topeak Road Morph (or Mountain Morph).
Water holders: anything will do
Racks: If budget permits, you cannot to better than Tubus. I like Tara front and Cargo rear, but Logo rear is also very popular. If budget is tighter, you can look for something less expensive, but make sure it is rated for your load.