If you use not any smooth shading on the surface and the area around the cylinder is not curved.. that should be fine.. ( maybe one additional support loop ad the 90 degree edges).. ..or: have a look at it with some light object.. see any difference.. ?
I guess thats one mistake that happens most of the people here. Try to create a object with many seperate parts. This may give you more objects but the modelling gets easier. Think of the scope as a real object. The ring would be turnable, so there is no need to model it as one object.
No, build your HP model as it is done in reality. If it's made of several objects, do several objects. Making 1 object is overly more complex and time consuming, and as you'll struggle with edgeflow, will probably doesn't look as good. Nonsense !
"...my low poly topology is atrocious. I've tried redoing it a few times, but I always end up with a similar result." hmm...well to start with there's a whole heap of redundant vertices or edges that are not contributing too the overall object's silhouette/shape. EDIT: So firstly I'd advise desolving those continuous…