Hm, well my girlfriends dad is into RC airplanes, so I’m sure he can point me in the right direction, not sure if I could find small enough props for the side exhausts, for some reason I think props looking more like ship props would look best on those, I might just get some lego ones as they seem to fit correctly.
Cheap plastic WW1 or WW2 aircraft kits? Plenty of choice on e-bay etc or have a good dig around in car-boot sales. They come in a variety of different sizes.
You would probably be able to cannibalise other parts such as wheels, engine doodahs, wings etc - especially from WW1 planes.
I always fancied making some steam-powered microlites from bits of 1/72 WW1 planes. One day, maybe.....