Sounds like you've got the plan down dude.
I'd jump in on the 10" barrel camp. I built my SBR with a 10.3 Noveske barrel. And just using an EOTech HWS, that thing is deadly accurate out to a couple hundred yards. Either suppressed subs, or regular supers. If you throw a LPVO on something like that, it's only going to get more deadly for those pesky 4 leggers.
That's great that you're getting your boy involved at that age.