Thanks for the clues, I'll try BanditUI. I was imagining something covering about a 100*100px area around the reticle, but maybe this will do or I'll tape something together based on those addons.
I happened to find a video of t3hasiangod with some circle around his reticle, it looks like it might be tracking resources?
https://www.youtube.com/watch?v=eamXIoFfGEA