I think you are going to love the Valley View power. They really make a great little engine and are fantastic people to deal with. I hope you have the room on the firewall to mount it inverted. It's a much cleaner installation. I switched to gas about 4 years ago. Once I ran out of nitro I didn't buy anymore. I have ran a couple of props on DLE20cc. The 18x6 Xoar is a good all around prop. I have a 20cc on a profile though and like the 16x6 Xoar on it. The throttle response is quicker with the smaller prop and for low altitude 3D type stuff it gives the profile a better feel IMHO.
When you order a smaller tank make sure you get a gas stopper. The stopper that comes with most tanks is for glow and the gas will eat it.

David