.223 is good for light varmit when using near match grade/60-70gr, it will still punch through 1/4 steel @ 800M but you'll have lots of drop and most likely max out your optic's elevation.
My .02 is look for .308, it hits hard, cheap, and isn't blown around as easy as .223. You are going to be spending the majority of your funds on your optic, which pays off in the long run if you get a quality Nightforce or Leupold. Limitations when it comes to long rage accuracy is often skill over equpiement.
One easy way to track the changing of blends without additional sensors or testing is to watch your long term and short term fuel trims in comparison to lambda granted you already have a legit calibration on E85.
My .02, you won't get anywhere near the robustness/reliability of an OEM with an MS based board unless you make serious changes with the matierials,traces,and some of the code.
One of the scariest things I've ever seen is a cylinder by cylinder lambda breakdown on a production V8 under various conditions. Going deeper into the rabbit hole, you really need a test cell to evaluate the whole picture. /.2cents
Congrats! What job did you enlist under? The armed forces offer alot of education oppertunity (skillsoft, landwarrior, etc). Stay fit, stay alert, stay alive. Be where you are suppose to be, on time, in the correrct dress.