John: you didn’t say whether you have done any paddling yet. If not, sounds like you can borrow some boats and try them out, or visit a kayak sales outlet located on a lake and try out one or two of theirs. I’d guess you want a long laker or sea kayak rather than a shorter river or white-water boat. Whatever, a kayak will give you a great upper body workout but unless you are very strong in the arms it won’t do much far cardio. Can’t be beat for enjoying the outdoors though ...

A long narrow boat can be surprisingly stable; I am your height but a bit lighter, I was around 210 when I first paddled, it was a 18 ft boat about 22" beam, looked awfully narrow to me at the time but stable as you could wish for and handled powerboat wash with aplomb.

Regarding multi-chine vs hard-chine, if you plan to buy a kit there wouldn’t be much difference in the amount of work. Hard chine boats tend to absorb rolling energy quicker, multi-chine might turn a little easier.

My boat is my own-design canoe, five planks, so that’s 2 chines, almost zero rocker and very sharp entry and exit lines. It is very easy to maintain hull speed or faster for long periods because it has low drag, tracks like a train and about as easy to turn. Although it feels tippy boat wash just passes underneath it with almost no effect on heel or direction. On a long trip I can rest on the water - went to sleep once but don’t recommend it - by hooking my leg over the paddle and using its buoyancy for extra stability - difference is amazing.

I built another similar canoe, not yet finished, with more rocker; the sheer is higher in the bow and lower in the stern, because the original boat tends to weathercock.

When making your selection consider whether you will want a sprayskirt, ability to roll, and where stuff will be stored - i.e., will you want to be able to reach it while in the boat on the water, or just when ashore. If you plan to fish from the boat, primary stability will more of a factor, as will storage of poles and other stuff within reach from the cockpit, and a place to park the paddle.

Whatever you decide, good luck!