So would anyone else have any recommendations as to firearms I should invest in?
Since you asked, 22 LR and shoot lots, spend your hard earned money on rounds not an AR15.
Myself and probably millions of other youngsters grew up shooting a Cooey .22 and I'm sure you could get one without breaking the bank.
The priciples of marksmanship are the same whether its a pistol or a sniper rifle.
I personally don't find the bite of the c7 bad at all, nor its noise. I think i'd probablly prefer to train on a weapon as similiar weight and calibrewise.
I don't know the specifics off the top of my head but a Cooey is similar in size to the C7.
Staying small calibre is a good idea, you could probably get an old 303 cheap as well but after 50 rounds your shoulder will try to convince you to stop.
You can shoot a 22 all day (if you have the rounds) and it won't hurt you, (you do need to keep aware of the barrel temperature).
As an aside the 22 isn't loud and if it's not a semi-automatic doesn't spit casings out as you fire, but I recommend ear plugs and safety glasses, protecting your eyes and ears is always a good call.