I would at least get a Seat Concepts seat for comfort, and a Cycleracks rack for your camp gear.
Other common mods are Bar Risers, Wider Foot Pegs, Shinko Trials Tire up front, MSR fuel canister, etc.
I'm sure you can equip the bike with all the comforts & must have mods for $ 700.
I have ridden my TW quite a bit around the Eastern Sierras, and I think you should have no problem making the trip from Mammoth to Victorville, especially in 5 days.
I'm sure you will need to hop on the 395 here and there, but since you already know many of the dirt roads, you should have no trouble navigating the route, to stay on dirt as much as possible.
I live in SoCal, but truck the bike 300 miles up to Big Pine, Bishop, Toms Place, Benton, etc, for base camp, and ride around from there.
Have done a few 150 Mile + days on the TW up there. I try and stick to dirt, & back roads as much as possible, but have no problem jumping on the Hwy for short jaunts.
The TW can cruise 55-60 on the Hwy, and when cars come up and start riding my a**, I just move over toward the shoulder and wave them past.
I've considered riding to Mammoth from Orange County, but I just wouldn't want to ride all that hwy, and it would take so long on dirt roads, I just don't have that much free time.
Id rather truck the bike up there, park the truck in a safe place, and spend more time exploring the area and camping off the bike for a few days.
My next trip will be up to Papoose Flats and Coyote Flats.