Building advice needed

Long time boat restorer, first time boat builder.

I'm designing a prototype for a single-seat, semi planing hull to fulfill a niche market in Sweden of business men that commute to their jobs by jetski.

LOA is 4m and beam is 90 cm, powered by an air-cooled 15hp inboard (gokart engine / got it for free). Note that this isn't a finished model, I have yet to add a rudder and interior layout, but it will be a single seat cockpit with a removable foredeck that can fit an additional seat or cargo bay

My main question is regarding hull thickness. I plan on glassing over the exterior and interior, and want it to weigh as little as possible, hopefully liftable on my cars roof rack... What thickness of plywood is the bare minimum I can get without worrying that my foot will punch through the floor?

Also, would you folks recommend frames made of plywood or solid timbers for such a design?

My expertise comes from restoring old sailboats, so really any advice or things that catch your attention is greatly appreciated!