4 gpm may not be sufficient to properly regenerate a water softener if you plan on one. Unless you have a rare well there should be aspects of your water you will want to treat.

Hopefully a plumber will chime in but "... a 75 gallon hot water heater and a 50 gallon hot water heater, but we also have a big tub and multiple shower heads" seems pretty demanding for only 4 gpm.

A well 6" diameter holds about 1 1/2 gallons of water per vertical foot. Subtract from 525 the static level of the water and subtract the distance from the bottom at which the pump will be placed for the usable depth of water. Multiply by 1.5. Let's say it is 445 feet x 1.5 for 667.5 gallons. That much is available without any additional inflow. and in the hour that it takes to pump that out, 240 gallons more will inflow. The average household uses about 200 gallons per day. And 4 gallons per minute is 5,760 gallons per day. Yes, I think your supply is quite adequate.

Install a large pressure tank - 4 gpm is perfectly adequate.

Thanks everyone!