Upgrading your TM is a good idea, I like having a little extra when I need that power. The swivel seats is good. If possible get some plywood 3/4" and use a marine grade varnish on the wood after cutting to size and attach it to the bottom of the seats, this will give the swivels a better base and a little more support. Storage of rods is a little tought there. You don;t want them sticking up, unless you have no other choice. Running them under the seats is a pain when needing to access a rod. Putting a rod holder running across the top of the seats is IMO your best option. But this also would mean running 2 rods in one direction and the other 2 in the opposite direction, this will keep the space then need as compact as possible. Cooler and tackle system, keep it simple. BPS sells a Bill Dance soft sided tackle bag that holds 6 of the 3700 Plano type boxes with pockets for smaller boxes. A great bag overall and this is what I use when fishing on someone else's boat. I'd carry a simple Igloo type playmate, something can can hold at least 4 quarts of fluid and a 8-10 pound bag of ice. Maybe one that can fit under a seat.