Any advice on where to start?
Ok, this didn't help me at all.
I don't know a good scope from a bad scope.
Names, manufacturers, specs to look for, features to get...
It all depends on what kind of shooting you plan on doing with your AR. Distance, target, CQC, hunting, competition???? I run red dots on my AR's, I've had Eotechs, Aimpoints, Vortex (to name a few). For red dots start researching those manufacturers.