I bought a 15kW propane Generac a few years ago, and there's a couple things to consider....

I would recommend going with a professional. If your neighbor helps hook it up directly to your power without a transfer switch, you're gonna have a bad time.

That professional can help you size the right generator, and the right fuel amount needed to run it. I use some big electric heat pumps, well water, etc etc for electric and already had propane water and stove and so I ended up upgrading to 300 gallon tanks. Propane lasts a long time so I don't have to refill the tanks more than once a year.

Run time is important. If you're OK having a few day's worth of backup, batteries are fine. We just lost power for 5 days and the propane lasted me the whole time. My neighbor's powerwall made it 3 days.

Price is also important. Batteries will run you less money in the short term, although they may have a shorter life than a generator with the wear if you have multiple outages per year. For my generator setup I paid about $12k for installation, propane work, electrical work, and the generator.