The 762 hits alot harder than .223, magazines are plentiful and cheap, ammo is plentiful and cheap.
223 is more accurate, recoils less, weighs less, is more expensive than 762 and good 223 mags are not as easy to find.
Congrats! You bought some awesome guns! And welcome!
There is no "factory" folding stock as of yet, but Rob. Arm. claims it's on its way.