They started with 6 tubes and welded several together end to end to end up with 2 tubes close to 40' long and 2 more in between the main tubes. So it's like a quadtoon.
"B is for build" on Youtube is building a Pontoon Yacht. When done it will be 40' long and 12' wide.
It will have a second level and a hot tub built into the bow. It's an interesting project.
Upgrading tires is good idea. Are you doing radials? Your boat will sit higher you will have to back in deeper at the ramp. Where are you getting your prices?
Pull the transom wood see how bad it is. Clean up all of the corrosion. Make one big patch and stick it on with 3M5200 and rivets. Install new transom wood.