Whenever you take marine ply and glue it together, only testing the engine at full capacity will tell you if it works. If the thickness is too large, then of course the motor will not fit onto it. You will have to coat it but here again it is called maintenance too.
regarding starboard, it is expensive but if you could find the thick pieces like on the Hunter 260, then that would be the way to go.
On starboard, it is hard to glue together but there was a trick I came with that even the mfg. was surprised. I use to glue pieces together with gorilla glue. You have to sand the surfaces and of course making sure they are clean of course. Then I applied gorilla glue evenly over the entire surface using a surated trowel and then applied together the two pieces and then clamped them together using boards on both sides and a lot of clamps. The first time I did that and threw a glued section hard against a cement floor, it did not come apart. I did have recessed bolts to aid holding it together after the glueing process which I let it dry for 24 hours.