A softener does not treat every tap in the house the same way. Before you size the unit or accept a quote, decide which water lines should be softened, because that answer changes the flow the softener must handle and whether the yard gets treated water.
Decide which outdoor taps stay on untreated water
Many households do not want softened water on the garden. Softened water carries added sodium, and many gardeners and landscapers avoid it for plants. Ask your installer whether the outdoor spigots sit before or after the softener, and whether the plan includes a separate untreated line for them. If an outdoor tap is downstream of the softener, get the plan in writing before the install, because adding a bypass later is more work.
Check the pool fill and top-up plan
A pool is a large one-time draw followed by a steady top-up. Filling a pool through a softener can push a lot of water through the unit in a short time, which can bring regeneration sooner and add to salt use. Ask the pool service and the softener installer how the fill will be handled, and whether the pool equipment manual says anything about softened water. Pool chemistry is a separate question from the softener, so get the pool company's answer before you settle the layout.
Ask how the layout handles each outdoor tap
Count the outdoor taps, note which room or wall each one feeds, and ask the installer to mark them on a plan. Confirm whether an untreated line can be added without cutting into the main supply, and who pays for the extra fittings. If the answer depends on the house layout, ask for a site visit rather than a phone estimate.
Size for the real draw, not the house alone
Size the softener for the indoor household first, then add the pool or irrigation draw only if the softened line will serve it. A unit sized only for the house can run short of softened capacity during a fill. Ask the installer to state the assumptions behind the sizing, and check whether those assumptions include the pool.
For the full sequence from first contact to final walkthrough, read the Missouri Water Softener Buyer's Guide.