First, welcome back.
Second, congrats on the FAL. Best main battle rifle out there...I have a DSA StG58 and a SA58 Para. They're awesome (I also own an M1A, a PTR91, CETME, buncha ARs, AKs, etc...I can honestly say the FAL is better overall than all of them...in my own humble opinion
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Next, I think the best deal going are the mags on DSA's website...excellent to new Steyr mags for $12. Next best deal I found were new-in-wrap military mags from CDNN...$7. The FAL mag is pretty tough...even the beat-to-heck genuine military mags I have are reliable.
Good surplus 7.62 NATO has dried up. At minimum, you'll spend $0.50 a round. I highly recommend reloading, but even surplus cases and projectiles are quite scarce these days. That said, I can load NATO spec rounds for $0.24 per round. In about 500 rounds you will have completely paid off your press, balance and die investment...then it's all gravy from there.
The Extreme Duty mount fits the StG just fine. The only difference in the SA58 and the StG is that the SA is all newly manufactured parts. The StG uses parts left over from the Steyr warehouse that DSA bought. New-old parts if you will. It is a great mount.
I like to shoot my StG58 with the irons. If you are going to put a scope on it, don't put a HUGE target scope...that just looks ridiculous and the FAL isn't meant to be a "sniper". If you want one optic that will allow you to have a variable mission, consider an ACOG or one of the low powered, illuminated variables...usually a 1x-4x variable. I have a Millett DMS-1 but other very good options are the IOR that DSA sells, the Horus, Leupold CQ/T, etc.
You can put an EoTech or Aimpoint on but the 1x optic doesn't seem to fit your mission.