RE: biggest amount of thrust without going over 18 amps.
Chris,
I had to laugh when I saw this post but I suppose that at one time you had a brushless motor to go with your controller. I'll assume that you are just looking for motor suggestions to mate with it.
I use a Mega 16/15/7 motor with an APC 10x4.7 prop which draws around 16-18amps on a 3-cell Lithium pack.