Why different membranes? Can you just not adjust the back pressure to compensate for salinity? That's how I ran my homemade water maker. When I built the system my knowledge of ro was limited and bought membranes recommended by manufacturer. I use separate housing for cleaning and pickling and then store them away. Membranes seem to last years for me so I never changed my setup as new information came to me. I get good tests and I'm happy with the water taste and the amount of time I have to run to make water. I guess I'm running on if it's not broke don't fix it.
Mods- Can you change the title of this thread to RO filtration for yachts, as there are only a couple replies to my original question and the rest is about RO Watermakers! Yet another derailed thread that has nothing to do with the original question or post.
You got your answers on the first page. Basically, don't filter City Water. Shocking the tank/lines once a year (I'd say 2-3 times a year in South Florida) with chlorine is also good to do. Carbon and particle filter at the water pump and UV steralization light and should be ok, perhaps second filter or brita at the crew spiket.