I had my first one-person show in 1985 -- 33 pieces, 20x24 frames and some 14x24 frames. I looked at it as an investment (about $1000 back then, including the mat board and glass -- and back then that would have easily been 10% of my annual wages). I still have some of the frames, but most eventually went with sold or gifted photos over the years.

So perhaps you should reconsider matting the 16x20's if that is your usual printing size...otherwise you could be stuck with frames that are too small.