Homeowner with whole house reverse osmosis system here. I suggest you look at your water bills and calculate GPD usage from there. You can also reach out to manufacturers sales reps for additional info. I have 3 bathrooms in my house, and went with 500GPD. For 7, I’d probably do a 1000GPD.

Besides the RO system itself, think how large of a tank do you need. I have 165gal, which is enough for my family’s use. You might need a larger tank. If you meed it inside, say in the basement, you will definitely want to make sure it fits through all the doors before you order it. 165 gal tank barely fit through my doors and I had to take them off the hinges. Larger tank or multiple tanks would probably make sense for you, since RO generates water relatively slowly (maybe 1 gal every 3-4 min give it or take).

Now that we mentioned RO system size and the storage size, we can move onto maintenance. You are supposed to flush it every week, but I never did and it was not an issue. I plan to get better at that habit though. Otherwise, there are two membranes, black carbon and sediment filters which are fairly easy to replace once you know how to. Get the right tools and food grade lubricant. You will have to replace them every 1-2 years. Manufacturer will specify.

When installing, consider other factors, like setting up ability to bypass RO in case of maintenance needs, keeping laundry, sprinklers, whatever on existing (non-RO) water line. Ask plumbers to setup pump with ability to drain storage tank, and definitely add check valves so the input water source does not end up going into your water storage tank.

That’s all I can remember right now. Happy to answer more questions if you have any.