I agree with Joe ^. Also how much current is your welder/ air compressor going to pull to determine the gauge of wire you need?
Say if you doing a 50 amp circuit, I would run 6 gauge 3 conductor(copper 60c) out there. If you hanging it, make sure the wire is UV resistant or it won't last too long.
Your garage is fairly close, I would think about trenching it out there. Put it in some pvc conduit and be done with it.
i'm looking at the acog 1.5x or reflex. i've got a 4.x32 acog on another M4. I want a CQ setup on this Colt.
the aimpoint stuff i wasn't crazy about, but that was from searching online.
And scott, that leupold looks nice also.