Wonderful job, This is our plan as well on our 40 year old Islander 41. We plan to start with the v-birth to get practice and then move to the main saloon and finally the aft stateroom and hallway.
I'm planning for some overhead boards with some 8/4 mahogany that I will trim down to 8/4 x 1/2 inch as trim and to cover the boards were we need overhead seems. I like the idea of using the PVC trim, its cheaper and will work well. Also plan to use 1 inch foam boards overhead for extra insulation. I found the aluminum insulation available at HD seemed to work well in our closet so may use that behind any exterior facing wall panels.