Hi Racer17m,
Tough question to provide a definitive answer...
Some folks use a small, 5.5 kW unit (
Onan Quiet Diesel), others opt for a monster 10 kW or larger unit (
PowerTech). Check out both of these web sites for some sizing tips.
More thoughts:
1. The lights and water pump will probably be 12v DC and, therefore, run off the batteries and not require a generator.
2. I opted for a solar-charged system with a large battery bank and an invertor. I do not have (and haven't needed) a generator.