16x20 is reasonable IMHO if you do drum development - I print in my CPP2 and can do 16x20 with ease. I could buy a bigger drum and do 20x24, but there's $300+ right there and I can't be bothered just yet. Your enlarger should definitely go to 16x20; the limiting factor will be processing space, especially if you use trays.
dev+stop+fix+fix+wash is a LOT of space if every tray is 17x21" or bigger. Stacking trays saves room, but you need to get a big wet floppy bit of paper between trays without scratching the surface or crinkling it in the slightest.
95% of my prints are 8x10 though. I buy that by the 250-box and use them to paper my walls at work, then they go in archival boxes for storage. The occasional Really Good Frame (maybe 3 per year?) gets printed to 16x20 and probably framed.