M512D

Welcome to the 308AR community. Large frame accuracy takes much more than a good barrel, perhaps some luck with build...Criterion hybrid heavy barrel 22" might be a choice. Attached are some borescope pictures (gas port, crown, breach, land). The machining and finish look great...I am sure there other good options...

Definitely FFP for long range as you can use the reticle for making measurements and calculating/making corrections. MRAD is easier for making the calculations on fly but no difference if you use a range finder and ballistic calculator. If you don't have a preference, go with MRAD. If you choose a high quality optics for long range, avoid quick detach mounts or anything that can add play in the system. The high end scopes are not just the optics/clarity of the image. They are also the reticle adjustment mechanism - accuracy, repeatability, reliability, shock resistance, etc. Check what others use for your intended purpose, avoid novelties...

What is accuracy of your 308AR build for 5-shot groups at 100 yards? "Only accurate rifles are interesting" - Townsend Whelen

Welcome to the 308AR community and congratulations for your new build. If you have not decided on the glass, my suggestion is to go with the best quality option you are willing to buy for the intended purpose/capability of the rifle. If you are not sure about MOA or MRAD, go with MRAD. If you buy a quality scope, get a quality mount...With the low recoil and high quality optics you will have a higher chance of seeing the impact and making an accurate correction...Good luck.