with an 16x18, you should be able to squeeze out 18. If you do 1 piece, you might manage 19, but depending on the price of the reel, that may be a negligible savings.
Using 1-piece stringing, you can string that racket with 33' (32 if you have a crank where the tensioner can get up next to the frame). That would allow you to string it 20 times.