Most likely the submersible pump is 240V, somewhere around 3hp. I can’t imagine it pulling 25-30 amps even at start up.
My thought is a 6500 watt generator should be more than enough. Maybe even smaller. Larger generator than required just means more fuel burn.
Also since the pump won’t be running full time, a generator with an auto idle feature would be a nice feature. Not many 240 Inverter styles available that run off propane without a conversion, but that would be my first choice. Otherwise you’re just going to be burning fuel for no reason.
Another option is a battery system, decent size 240V inverter/charger, and small inverter generator to recharge if necessary. That will likely cost a lot less, and burn a ton less fuel. Somewhere around $3000 all in, even with pass through with an auto transfer inverter /charger.
Here’s a cheap one on Amazon that will give you some ideas.
https://www.amazon.com/SUNGOLDPOWER-4000W-12000W-Input-240VAC/dp/B088R4WLJQ
