Welcome! If your engine doesn't have recommended prop requirements and since you have a trainer, I'd start with a 10x6. If after a few flights it's feeling a little sluggish on take off's or climbs, change over to a 10x8. As far as props are concerned, I'd recommend the APC brand, but that's my opinion. Here's a link to help you out. http://www.flightlines.com/introduction/propchart.htm