Huntinfool, I added the pontoons to the boat for 2 purposes, 1) To give more flotation to the rear of the boat to help support the 80 hp Merc., the pontoons are also filled with spray expanding foam to give even more bouancy. 2) To aid getting in and out of the boat on the water, which is why they are stepped.
There was no real design I went with as far as how big to make them except to allow for side to side movement of the motor while steering (which determined how wide they could be). When I was building them they looked big on the fab table, but on the boat they don't look as big, I kinda wish I made them a little longer than I did.
Starting a Tin Boats Club around here would be cool, just don't know how many guys around this area would be interested? Meet & Greet could get things started. I am game for either.
When you say livewell, are you talking for bait or fish? I don't use a permanent livewell system mounted on my boat, In my opinion they take up too much room for a Jon Boat, I use a cooler like the one in previous posts with either the oxygen system or the aeriated system as described. We sometimes use my rig to just go riding around / pleasure cruising so I dont need to haul a livewell cooler all the time, just when I am fishing, plus this cooler doesn't take up too much room on the boat. If you choose to make a onboard permanent system I would insulate it somehow, every little bit helps to keep your bait fresh.