Absolutely awesome you are taking your 250 Sherpa on a two-continent adventure, and even more so starting from home! You are blessed to have the time and health to do the trip, as well as the sensibility to realize that you don't need a 1200cc adventure bike to have a real adventure.
During my rides in the Peruvian Andes last year and Costa Rica this year I did the Fly & Ride approach. I had a blast, no regrets, but I sure missed my little XT225 when the big rented bikes got into some of the heavy stuff (especially when they were horizontal).
Have a fantastic trip; I will certainly be following from home.
All the Best,