Re a spare tire--i've toured since 89 and only have taken a spare tire when touring in Latin america, rest of the time you simply make sure that your tires are in good shape and you use your eyes and don't ride into obvious stuff.
just be normally attentive and for obvious reasons, don't ride through a scrap metal yard and you'll be fine, seriously.

re effort etc, as you noted compared to riding unloaded, downshift, downshift, downshift
18 wheelers shift a lot and don't lug the crap out of their motors, don't lug your knees and legs.
plan very reasonable daily distances, 30 40 miles, and take it easy.

internet asking is one thing, but like others have said, you'll figure out your stuff by doing it.
taking notes is an excellent idea.
I too hate being cold, and why I always bring full rain gear, jacket, pants and rain booties, cuz even up here in Canada eh, summer storms can be cool and being all wet is blah. (My opinion comes from numerous times of "been there, done that"----but hey, no matter what you do, you won't die, so go and see what works for you.

safe riding

oh, use a mirror eh.