I built a Tern and have size 12 feet (the rest of me is 5'10" and 180#.) I found there was plenty of room, but I also wear neoprene booties and not full shoes. Personally, I think you'd be fine in either the standard Tern or Coho. If you found it snug with your size 13 shoes or sandals, I think going to neoprene booties or aqua-socks would do the trick.

I built my Tern not having paddled one; actually I had only paddled one rental plastic kayak. After paddling the Tern for my first season, I felt it was a bit too big for me so I built a low-volume Outer Island strip kayak. It was recommended that I add 1/2" to the height of my deck to compensate for my size 12 feet, which I did, and it is comfortable for me. My point is that I've downsized to a kayak that's a good deal smaller than my Tern and haven't had problems with footroom. I've even paddled (briefly) a 20" beam CLC North Bay and don't recall having footroom problems (although after a few hours I might have wished I could have moved my feet around a little bit...)

Dean