For 4 people with 2-1/2 baths, a 50 gallon or 75 gallon residential water heater would be just fine. Depending on the locations of your fixtures, a recirculator will come handy.
I was wondering why you were pondering and leaning towards a commercial water heater.
Just a WAG here, but...
The all stainless condensing Phoenix LD will outlast a glass lined (standard or condensing) gas-burner by at least 2x in a residential application, and the modulating 25,000- 76,000 BTU/hr burner guarantees rapid recovery, but isn't insanely oversized for the application like many/most commercial water heaters.
It's also enough burner to run a hydronic air handler (or micro-zoned by room with individual fan coils) heating system for a tight 3700' house in Maple Valley with burner to spare for water heating. This is well worth pondering during the design & construction phase of the house, keeping tabs on an aggressive room by room Manual-J heat load calculation. It might take a slightly larger-burner Phoenix to do it all if it's a fairly lossy house with a code-maximum window area using code-minimum windows, but if built to IRC 2015 code minimum or better with a "reasoable" shape and "reasonable" amount of glass it's likely that the true heat load will come in under 40,000 BTU/hr, and you'd still have 36,000 BTU/hr of burner to spare for heating hot water, which is roughly the burner capacity of a typical standard 50 gallon gas-burner. It would be key to not oversize the air handler's heat capacity by a whole lot and/or use a modulating air handler- you don't want it to hog the burner capacity just to have enough to heat the place to 70F when it's -25F outside (an outdoor temperature than hasn't happened in Maple Valley WA since the last ice age.)
For the record, I heat my place hydronically with modulating tankless water heater set up as a boiler. The biggest zone (by far) is a 1-speed air handler that delievers ~38-40,000 BTU/hr at the ~125F water temperature I'm feeding it via a 48 gallon buffer tank (that has an internal coil heat exchanger for the potable hot water.) Even though tankless the water heater is capable of delivering well over 100,000 BTU/hr, as-operated it never exceeds ~60,000 BTU/hr, even when somebody is taking a long shower when all zones are calling for heat. (My 99% design heat load is between 35-40,000 BTU/hr, and at showering temps I'm radiation limited to about 45,000 BTU/hr out of the air-handler, radiant floors, and radiators- yes, it's micro-zoned.)
Doing it with a Phoenix LD would have been simpler, cheaper, and at least as effective but it didn't exist back when the system was designed.
A recirculation system might be worth it for a 3700' ranch house with the kitchen & laundry on one corner and the master bath on the opposite corner with very long runs. But if it's a 2-story house running the hot water with smaller diameter home-runs to a manifold near the water heater keeps the lengths & wait times well bounded, and is generally more energy efficient.
