Upgrade advice

I second the family friendly, casual guild. He will have a much nicer time grouping with a few friends than a random set of people who are rushing through content.

The flying mount is a big milestone, and will be great fun when he gets it.

I'd have him go back and pick up skinning, and maybe mining or herbalism. He will need to go back to earlier areas to start the professions up from scratch, but he will quickly be able to skin or gather resources in his current zone. Get the addon "Auctionator" from curse.com (I recommend the curse client to manage addons). Use Auctionator to sell the mats he gathers on the AH (there will be new buy and sell tabs on the bottom of the AH window). Just to reiterate, never buy gold. Doing so cheapens the game and robs you of the feeling of accomplishment.

I hope your son enjoys his time leveling. The first time through can be amazing.