The BFR should be downscaled to 5 meters becaus the bluedog design bureau Saturn V is around 5.16 meters across, and the real BFR is of a similar diameter to the Saturn V.
Making the engines compatible with realplume would be great for cinematic videos about the BFR
Realplume is a mod that makes the plume change with altitude and makes it look way better, the hydrolox plume would be the best approximation of a methalox plume