You seem like a nice kid. Almost like me when I was your age. A hard working, straight talker (you don't seem, "wishy washy" at all) and you're really open about your intentions.
A really GOOD upgrade platform would be the Kraken AK-47 since it's cheap and you can put a lot of work into it to get it upgraded and whatnot (it's actually a really sweet upgrade platform IMO).
If you are really intent on getting an AR-15, may I suggest getting the M4 and going the C8 route?
Also, a "better" father son project might be making a cedar strip canoe (I did that with my family).
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE