You can buy it from your account then he can log in when he gets it, don’t buy it on his account or else he’ll automatically get the shipping information emailed to him. Another important thing to note when buying it as a gift is that although the box it ships in doesn’t say steam deck on it, it has its own standard box so if he’s been considering buying one himself and looking at reviews or unboxings be careful as he might recognize the box if he sees it
I always pause and save then turn put it in sleep but not actually close the game