We have a 9+ gpm tankless (NG), it just needs regular 20A service. If you can have a propane tank installed and get a tankless, I highly recommend it. We can run 3 showers at once, all day long if needed be.

The tankless is in a small crawl space over my porch, accessed through the back of one of my wife's closets. It could easily fit over the washer for a small home. Get a couple of quotes from propane supply companies for the install, see if it is worth it.