Lot’s of respect to you for trying to modularize a ship
I think it’s possible, but it will be very complex.
I think your idea of splitting it into front, middle and back pieces is going into the right direction. But I would try to not place masts for example, as these could be placed by the user, making it even more modular. You could also try to seperate the outside faces of each front, middle and back pieces (I mean the side where the canon windows etc. are) from the actual area, where you stand on and walk around. This would increase the modularity even futher.
For each front/middle/back piece you might also want to seperate the upper most level from all interior levels, since you might want to build them differently on the inside.
And I think you should make the tip of the front piece seperate as well. and maybe add a basis for adding statues to the tip.
Aside from that, you could increase the modularity by properly grouping mesh faces together, so that users can apply different materials to different components of the ship, like using different wood materials for frames and planks.
Is this going to become a complementary pack to your modular ship props pack?
I am going to keep an eye on this and buy both packs, if it turns out good