Another vote for the 8" Dob
My son got one for his 13th, too
Regarding the anything else bit, those Dobs come with all the necessary accessories to get him started. Beyond that the sky is the limit and he'll find plenty of things to spend his pennies on (like with any other hobby).
In hindsight (having bought one myself way too late), the first accessory I would recommend buying is a height-adjustable observing chair. The difference this makes to what you can see through the telescope is much bigger than the difference between the included eyepieces and some $300+ eyepieces (which for many beginners are the first accessories they lust for).
Cheers
Steffen.