It is actually fairly simple. Many sellers have "max amps", Recommended prop size, and max battery size. IE 1, 2, 3, cells referring to lipo.
You have a 25 amp esc. You look for a 20 amp motor swinging a 9 or 10 inch slowfly prop and you will be perfect. If you figure for a 3 cell motor. as long as your esc can handle three cell you will fly for a long time and never have heat issues. especially if you throttle back.

Kv rating is rpms per volt.

if the motor gives max watts then watts/voltage(battery used 3 cell 11.1)=amps.

The hobby king website is really good about that so can you can make sound decisions on decent information. Plus you can get a pretty good price too.