Instead of guessing, why not measure the static thrust with various props? Mount the engine on a a large board. Put dowel rollers under the board and measure the static thrust with a fish scale such as a Zebco Deliar. Pick the prop that gives the best static thrust. If the plane you intend to build weighs less than the static thrust, then it will be able to hover. The less the plane weighs than the static thrust, the better it will accelerate vertically.

The size of the wing will determine how slowly you can fly the model. Once you set the target weight of the model, you can calculate the wing area required to give it a wing loading in the range of 20 to 24 ounces per square foot (good for 3D). Having the wing area, when you pick an aspect ratio it determines the span.

Once you have a target weight and wing size, the trick is to build an airframe that is strong enough and light enough to carry the engine, fuel, radio, landing gear, flight loads, etc.