I bought mine like this, they can be swapped around like the drivers and clutch but it's not recommended its easier just start out with the left hand drive one in the first place
No it has to be a specific freecoaster hub, you could ride chainless to get an idea of balancing going backwards but other than that it's either a freecoaster or cassette
If you swap out the rhd driver and clutch for a lhd one the hub will screw up and the big bearing behind the driver will come out of the hub shell and the hub would be toast so just save yourself the hassle and money and just go for lhd in the first place