Water methods

gonna be all kinds of scales. not worried too much about scale lining up. these would be full hull models. put plywood down, paint, then cut and add gel as needed?

I'd like to suggest just using ply and paint the whole water area whatever water color suits you and then use acylic gloss medium to add waves and wakes as you add your ships. What scale are you considering? Of course this works best for waterline models.

That is a good approach for waterline ships.   Go to the lighting department on your local home improvement store (Lowes/Home Depot) and get a flourescent light fixture light diffuser panel.  These come in several textures -- they have several types including one "cracked ice" which may do you well.   The one over my head right now is too even a texture to use as water.  Get what looks good to you.  Flip it over and paint on the textured side.  Paint it a harbor blue-gray color.  The panels are 2x4 feet

Position the ships on the smooth side without cutting holes in the sheet.  By this method you can reposition the ships without having to deal with holes.  It allows you to grow your fleet and display it as it best suits you.  

If you choose to display whole hull ships in this manner, you can still go this route.  The plastic cuts with typical home woodworking tools.   Trace your ship hull (measure twice, cut once),  drill a starter hole,  jigsaw out the hull shape, file & sand smooth