That’s a very big question.
Own boots- I’d say no until he knows he wants to carry on skiing as a properly fitted pair of boots is £500+.
Gear..TK Max have sometimes got some decent stuff. Decathlon is budget but good. Go Outdoors have some reasonable own brand stuff. Online Revolution Race are very good for the money. Snow and Rock/ Cotswolds Outdoor for a decent high street experience.
Decent merino wool socks, merino thermals, decent gloves and I’d invest in his own helmet and goggles.