Grades: Yeah I learned from someone that knows trains, typical train routes did not exceed 4%, it's really hard to get enough friction for climbing with steel wheels on steel tracks in the rain. So even in hills and mountains, an old train route will thread a path through that is gentle. 2% is especially gentle.

Rim brakes: Yeah I put in serious miles on a road bike with rim brakes for a decade in flatland, never even wore through the hard anodizing on the rims. Just barely used the brakes, but I also only biked in the dry, on pavement. That gravel trail is a lot more grit, but again, slight grades and no sharp bends, that's the saving grace, don't need to use brakes hardly at all, I would imagine.

Train trip: My limit for sitting is a half-day, the seat bottoms felt hard, not very ergo. I could go longer if I could sleep horizontal, but sleep cabins are really expensive, more than airfare. We need cross-country high speed rail in the USA for major arteries, but that's never going to happen. Few need it except us bikers. I'll figure a way to transport my bifolder by air, it's just gonna need two cases to fit max checked size without fee on airlines with free checked (some airlines now don't charge oversize for bikes but still charge for checked), and the hard part, is where to stash them while biking, assume I return to the same airport. And trying to fab cardboard cases each time is a pain. I wish the airlines had standard padded soft cases of rinko size but without need to remove fork, that could be rented for a very nominal fee which would also include special handling between baggage check and plane, and you just show up at the airport, fold or partly disassemble bike, put in case, done.