Parallax is not a problem if you buy a good scope - Nikon, Burris, Leupold, or better. Eye relief can be adjusted on most scopes, even the cheap ones. The eyepiece adjusts. It is attached by screw threads to the body of the scope, and you can change the focus by screwing it in or out. There is a lock ring so that you can secure it when you have it set properly.
The proper way to mount a scope is with the shooter present. The eyepiece adjustment controls the focus on the reticle (crosshair.) The shooter should be able to mount the rifle and immediately see a sharply focused reticle. If the reticle is fuzzy, the eyepiece needs to be adjusted. Or the guy needs glasses (this has happened to me.)
Is there a specific rifle and scope combination you are considering?
I've got a Winchester 54 .30-06 and the scope I put on it is a Bushnell Trophy 3-9x40. Not exactly in the class you were talking about. Although I do need glasses for close work, I'm fine with the reticle and naked eye. It's that bright big circle that I can't get immediately.