I agree with D2B, you are the guy who knows your fishing needs. Is the livewell going to be used for live fish storage to hold for tournaments, or just as a live bait keeper?
I would consider putting a pair of big coolers in the lounge spot, one of them plumbed up with a drain through the deck or out the side and a pump on the back of a log to send some fresh water to it. That cooler will become your livewell. The big coolers come with mounting hardware and some of them have cushions available so the coolers can be used for seating. Through hull fittings designed for boats work very well to plumb coolers for livewells. You can make it a simple or complicated as you want, with aerators, diffusers, recirculator pumps whatever you want. I always had a cooler plumbed up for a baitkeeping tank when I fished from pontoon boats in the past.
A pontoon makes an excellent fishing platform, there is plenty of room and you can rig the boat with trolling motors, rod holders, everything you need to fish in comfort.
Welcome to the pontoon boat family and the PDB magazine forum.
2006 Forester 19 Fish (new deck and carpet, Pontoonstuff interior, 2019)
1996 Mercury 50 ELPT4S
1983 Sea Nymph FM171 Striper (complete rebuild from hull up, 2014)
1985 Johnson 70 J70ELCO
Raystown Country, PA