Once you add up all of the loads that will be on at the same time, the bare minimum you need is one who's surge amps at the required volts is at least 50% more than that number. Start up is real hard on equipment with a generator that is marginally sized. If the start up surge approaches the generator's surge max, the equipment is starved for power, that is the hardest on the electric motor. Get the specs on the RO both amps and volts and we can help.
When I was using a generator, I sized them so the max start up amps was still in the stated running amps, for my purposes the surge generator capacity was just an extra reserve.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.