Peter, Winter Island Yacht Yard, installed a generator in my R 29. The boat had beed ordered generator ready. Came with the selector switch in the electrical panel and had the fuel tank, lines, and transfer pump installed. The exhaust and cooling water intake had to be installed. He chose to install a larger sea strainer for the air conditioners and connect the genet to that strainer.
Everything works well. The generator is a Kohler 6 KW. If you add all the electrical requirements for the boat it seems reasonable, but I can tell you that when I plug the boat into shore power I usually connect Line 1 and Line 2 with a Y connector and feed both from a single 30 amp connector. I have never blown the feed breaker. This tells me that 6 KW is over kill however it was the smallest 1800 rpm diesel marine unit available from Onan or Kohler at the time.
Kohler is now selling a 3600 rpm 4 KW unit, and another 3.5 KW unit is available from Whisper Power USA (whisper power.us) both have the same noise rating as the 1800 rpm units but are much smaller, lighter, and sip even less fuel. I use about 0.3 to 0.5 gph.
If I were doing the install now I would seriously look into one of these. I may not be able to start everything at once but I think either would power my boat just fine. Note I have the gas stove. If you have electric stove or grill you may need more power.