Not into LD rides but do do 5-800 mile days when on the road.
Have made 3 coast to coast trips so far on my 02 LT.
You can make the best time when traveling alone, additional bikes or passengers just complicates matters and doubles chance something will go wrong.
Leg aches -- try "Surburban" Lowered Pegs and XL "J-Pegs" so you can vary riding position and stretch out. I use the stock seat with a "Beadrider"
Neck pain -- excercise as you ride as mentioned, perhaps new helmet (love my Schuberth C3) and use a neck scarf/sleve to keep air off the neck muscles and keep muscles warm and loose. Scarf also adds support to bottom of helmet taking strain off neck muscles.
Shifter linkage -- When mine broke I was able to remove broken stud by threading it thru and out the back, then reversed linkage and reassenbled as there was just enough thread left to reattach (lucky break?). Then ordered replacement from [email protected]
and carry my stock linkage for a spare. I did manage to later break philjohns but I have a heavy foot and think his part is worth paying for so ordered another.
Carry an MSR bottle of extra fuel in case you misjudge gas stops.
Carry ready to consume food you can eat while refueling and stay hydrated by continuosly sipping on a Camelback, I carry a water bladder in my Cortech Mini tankbag.
Inspect/upgrade your lighting, front and rear. I have HID low beam, LED motolights and Kizan racklight flasher. Running lights on fairing and in tail light converted to dual elements.
Stop for at least one good meal/rest per 1000 miles.
I always start any trip with recent bike service/inspection and new tires.
I would carry Final Drive rebuild parts or find someone who has a spare drive you can call and could overnight to you just in case.
BTW: I just had the breakhose from the handelbar to front wheel fail on my 02 at 85000 miles. If you inspect up under the fairing where it attaches to the splitter block to both front caliper hoses and turn the handelbars you will notice how the hose (at least on my bike) flexes right at the steel collar and not along the length of the hose. IMO the routing or length of the hose creates a stress point where hose must eventually crack.
I would carry a spare as I had no luck finding a replacement when I was on the road ( I was in Deluth, Minn and A & S in CA was the closest dealer who had one on the shelf) . It's replaceable without removing fairing if you are flexible enough. I rode home to CA using the rear brake only since my 02 has linked brakes without issue.