We installed a whole house generator in 2014 and it's been great, in fact it's on hour 33 on the current ice storm emergency.
Maintenance - one oil change a new battery in 2022 and a leaky oil pressure switch. After today's run it's earned another oil change.
Size of generator needed - don't size based on house square footage, do a load calculation.
Whole house vs selected circuits - Money saved on a smaller unit vs added installation labor this is an easy call.
. Exception; if you have unusual large loads like a pool or dust collector or electric vehicle charger.
In those cases there may be relays to protect the generator from overload. ex; our electric clothes dryer will not restart unless the start button is pressed. If you have electric resistance heat it might be worthwhile to feed those circuits thru auxiliary relays which you could restart circuit by circuit based on need and capacity. Others to consider; water heater, stove, heat pump, hot tub ...
Noise - yes, unfortunately on the hottest, quietest night of the year when all the neighbors are sleeping with the windows open we will be running a loud machine and enjoying a/c. We installed a couple of 120 volt outlets on the back of the house and showed them to the closest neighbors inviting them to bring an extension cord to plug in whatever, no need to ask. Each is on a dedicated 20 amp circuit. A lamp, tv, phone charger, fan, a neighbor who cares, these can be a comfort in stressful times.