Once the bike is tuned up and ready to send, ride it yourself for a week. That should bed in all new cables and take the shine off new tyre tread and brake pads. Then check the shifting indexing last thing. Bed in any disk brake pads too.
If the rider lacks basic tools, prep some. Two tyre levers and a spare tube and a minipimp tjatminipump that fit the valves.
Add those white clip-on spoke reflectors and a rear one - unpowered means no batteriesred reflector. They often get "lost"
If your brother EVER intends to ride at night or in the dusk/dawn, then advise him to buy lights. However I would not include lights with the bike because they can get really expensive and might never be used.
If he does ride at night then you have a good idea for the next birthday/etc present.