1) Yes... just make sure the tub is STURDY and can hold up the weight of a fully filled Remora. Make sure that you add extentions to the pump so that the skimmer pump is always submerged in water.
2) Partitions are tough in a rubbermaid. If it were me, I would try plexiglass or pieces of plastic and use aquarium safe epoxy to attach. Don't know the exact materials you would need though. Just don't use glass... won't stick to plastic.
3) No need to cycle the sump. Fill it with freshly made water and that's pretty much all you'll need to do. Make sure it's well mixed and aged 24 hours at least, and that it's up to temperature. Make sure to test the power shut-off and see that the sump can handle any water that flows back from the tank. Try this at least a few times.