I am in the market for a feathering 18 by 16 right hander - in Fiji at the moment. I had a 17 x 12 fixed left hander fitted in New Caledonia as an emergency. It's fine but makes an annoying whirring noise.
You don't have a choice of LH or RH props for saildrives - they all go the same way. If you are going to buy a feathering or folding prop there are many different designs on the market so you need to decide what features you want and ask the manufacturers to recommend the size to suit your boat. The size you are suggesting sounds too small, but it does depend on the design you choose.
The whirring sound is quite normal for standard fixed blade saildrive props - it is the prop turning the gears when under sail. You can stop it by locking the box in reverse. Not recommended by Volvo but many people do it. With a folding or feathering prop you can lock in gear because the shaft does not turn. However, usually the blades will fold or feather if stopped in gear and then put into neutral.
