personally, what i would do if im planning this trip is bring a small pop up tent and a good sleeping bag, as this is going to multi day trip,
if you have a 3 wire cdi, get a 6v headlight and wire it up to the magneto, so if your going to be night riding you can see where your going.
i would gear the engine so you arnt revving past 5k, (ie you want 24mph, gear that so its your criusing speed, so you arnt pinning it, id go 40, maybe 36 if you can help it pedal up those hills)
good quality name brand tires, kenda, maxxis, csk, there all quality tires, id go with some maxxis holy rollers, heard they last a long time and the tread isnt going to lower your gas mileage.
pack some QUALITY 2 stroke oil, as i really wouldnt trust some gas station stuff, hell, i dont trust there gas half the time
also, have you planned your route on where you want to go?
(ie do you want to skip Idahos national forests all together? or do you want to see the whole thing?)
and, have the cash and a passport incase things go to complete s**t and you can just book a plane ticket home (if your bikes completely fails, and you just give up)
but thats a last resort, and we dont want that do we
if you do plan on doing it, take pictures! itll be the best adventure of your life!