Thanks all, this has been helpful.
It sounds like most battery makers will work. The charger should be a simple choice (Thanks, Latency - I'll look into the local R/C shops to see what they carry first). Once the gun is operational, I'll give the irons a shot (no pun intended). Depending on accuracy/acquisition time, I'll decide then if an optical would be required.
Also, thanks for explaining the mid/low cap mags. I thought all mags were setup like hi-cap mags, hence my confusion. My personal preference (back in the day, anyhow) is towards lo-cap for hard simulations, and mid-cap for everything else.
Sling question - The mounts on the SCAR appear to be based on the 3rd gen model, which are too narrow for most standard sling hooks. I prefer 1-pt slings, but I think I may need to use a MASH hook to secure it. A second option would be a 2-pt sling with a rail mount loop attached somewhere up front, and a buttstock adapter. (Although some folks have mentioned the use of paracord loops, I am not considering it.)