If you get a bill of sale when buying a used one, should not be an issue registering it as I went thru this just last month. I bought a used Nucanoe Frontier 12 with a TM already on it from someone in NC, got a bill of sale at time of sale, took it to the clerks office, a few minutes and $50 later, had my TN paperwork, 2-3 wks later, had my #'s from the state.
Since you plan on having a TM, look at the Nucanoe's, they have elevated 360 seats which may be helpful for you, very stable, can get a stand up bar for flyfishing, you're not "pinned" into one seating position, which can be low, making it difficult for older guys (like me) to move around, shift cheeks to relieve pressure points/numbness, etc.
I have a Ride 115 for sale listed here, and the only reason I'm selling it because the seating arrangement just does not work for me anymore. You can stand up in the Ride's, put a TM on them but you lose the rear "baitwell" area immediately behind the seat, or reduce it quite a bit due to the battery. The seat is comfy and has lots of adjustment, but it doesn't work for me anymore as I started getting uncomfortable after 30 minutes due to back issues. It was VERY comfy when I bought it but my back changed on me.