This is a interesting conversation. I have a lot more experience of making smaller steam locos, and the customers I build for usually don't expect a 2-4-0T loco from 1880s to pull 12 bogies. It's physically impossible to fit a massive motor in one, so something akin to a 1833 is your best shot. It needs electronics, say a V5, a stay-alive unit and a sugar-cube type speaker, which doesn't leave much room for ballast. I try to shoot for 750g (total mass) and that way the loco will comfortably pull a couple of coaches, as it did in real life.
I suspect the second motor is to pull the mass of lead added to give you the adhesion. Why not look at your stock? A well known modeller I once built a Princess for had coaches that were not very free running (poor/no bearings) and each coach weighed in at around a kilo. Perhaps that could also be part of the problem.
I suspect that there are modellers running 10000/1 in a consist of 4 motors (plus roof fans, hefty speakers, lights etc) needing a small sub-station to supply the amps?
Bernard, here's a Princess I made hauling a massive train up PW's steep hill.