The electrics can be a bit confusing. We all got accustomed to glow engine displacement and the very narrow range of props they are able to use for a certain displacement. Current brushless electrics are far more flexible. First thing is that the motor does not care which direction it is spinning. Back in the days of brushed motors, the timing of the motor was determined with the contact location of the brushes on the armature. With brushless motors the timing is purely a function of the speed controller. In some cases with the larger setups the timing is user adjustable. Faster spinning inrunner motors require low timing, 0 to 5 degrees while the lower rpm outrunner motors such as what the OP has requires high timing, 20 to 25 degrees. Most of the lower cost, smaller stuff will be plug and play but you do loose a little bit of efficiency. In order to select the correct size prop you need to know the KV of the motor, what voltage you will be running, the motor diameter and the motor length. For example one of my electrics has a 63mm diameter with a 55mm length. The KV is 230 and I run a voltage of 38v. Multiplying the KV x V we get 8,740 rpm. The prop selected is a 21.5x13.5 delivering around 2,700 watts at about 65 amps. If I was to lower the voltage ( thus rpm ) I could fit a larger prop and if I upped the voltage I would have to go with a smaller prop to keep amperage draw the same. I am going to assume that the batteries selected by the OP are going to be 3S or 11.1V, knowing the diameter of the motor and the KV would allow a prop size recommendation. I suggest looking at the APC web site to select props. Robert has in the past few years introduced a number of multi Rotor prop sets in various sizes that may work very well and are quite inexpensive. They come in sets of 4 with two being CW and two CCW rotation. As far as how to set up rotation, I would do some experimenting but I suspect you will notice little or no difference. Good luck with the project, the OV-10 is one of the airplanes that I always liked, Cal Fire has a few flying close to my home often.