My suggestion is do nothing except put lots of ammo through that new Glock. If he waits until he figures out what he likes and doesn't like he'll make better decisions. I have three Glocks that are basically stock and have concentrated on buying ammo, magazines and holsters.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek