Aside from the need for a clean, slippery fuselage ahead of a pusher prop to keep the airflow as smooth as possible into the prop, a pusher layout results in more net torque reaction on the airframe. In a tractor layout, the wing and stab act as flow straighteners of the spiral propwash, and in the process, cancel out a lot of torque reaction. For example, engine torque can be completely cancelled while hovering simply by deflecting large chord, full-span ailerons against the torque; Hovering, hanging on the prop with no roll would normally be impossible with a pusher.

I almost built a pusher pattern model, but had second thoughts at the last moment, when I realized that in a crash, the heavy stuff tends to find its way forward, smashing whatever is in front of it, and a rear mounted engine could make mincemeat of a fuselage in a relatively gentle crash that might result in little damage to a tractor layout. Always bear in mind that if you're going to fly, you are eventually going to crash.