First off, Good For You, getting him into shooting sports.
I I got my first bow, & first BB gun at a young age, & I also got my first hunting rifle of my own, a 30-06 shortly there after. Somewhere around the same age as your lil buddy. I never had issues with recoil, but I think where your headed with the brake is an excellent idea. Especially for shooting prone!
Id look at Jim See's Muscle brakes, namely the mini, the 3 port, or his new one inbetween those two. The case volume doesn't dictate any bigger of a brake, & the mini will handle the WSM family, so the -06 is a shoe in. Plus it doesn't add too much muzzle weight.
I here great things about Kirbys Pain Killer brakes too.
May I also suggest a limbsaver recoil pad in conjunction with whatever brake you choose as well.
My Winchester didn't have a brake or a recoil pad, just a hard piece of rubber. I shot mine just fine, but id have shot it better, I belive, with at least one or the other of these.
Then again, my cousins old Savage -06 kicked harder than any rifle I've ever shot in my life. That includes a 460 Wby mag, 340wby & 338mags 300 Wby, & win mags, & a pile of others. That thing was just plain viscous! I still cringe just thinking about that boat anchor!
As far as # of loads per case, well, you can load quite a few on an 06' with a reasonable performance/pressure compromise.
A way to check when to pitch them is to take a pic, or small piece of wire bent at 90* & scratch the inside of the case just above the Webb, feeling for a small crack, Before its evident on the outside of the case. You may feel a bump, or a catch in the brass case wall. That would indicate to throw it away.
Good luck, & tell that buddy of yours were proud of him