I have used RP brass in my 7mm-08. I have not had to throw away a single piece that I recall yet. I have loaded about 5-6 times so far. I have had to trim it a time or two and I also removed the flash hole burrs with a Sinclair deburring tool.
Several years ago though, I decided that I needed "better brass" and bought one box of 100 Lapua .308 brass. I will say that it is really good brass (and I don't have to "deburr" the flash hole). I neck it down easily and I have not had to trim any of it yet in about 3 loadings.
As for reloads, I think that you will find the 140 Ballistic Tips, 139 Hornady SP, 140 Sierra Game King and 140 Nosler Accubonds to be very accurate. Varget is a terrific powder as is IMR 4064 and RL15.
I also loaded up some 100 grain Hornady bullets for fun and they shot well with IMR 4064.
If your son is shooting the 20 gauge well, he shouldn't have any problems shooting the 7mm-08 with hunting loads. As others have suggested, you should have good hearing protection and definitely use a PAST recoil shield if he will spend very much time behind it at the range.
My 13 year old son shoots my 7mm-08 with Max charges and isn't bothered by the recoil at all. He is pretty small and weighs about 80 lbs. He also shoots a 20 gauge, my 12 gauge on occasion and didn't seem to be bothered in the least shooting my 7mm Rem Mag. My point is, he started shooting a 20 gauge and a .22 and has never had any real recoil sensitivity to shooting the larger guns. Your son will likely be the same way.