WRT the "range finder" it seems the lower end binos that are advertised as having a "range finder" actually just have a reticle with a scale that is graduated in mils that you can then use to calculate range. Which I'm fine with, I used binos like that in the military so I'm comfortable with how they work.
As far as power goes, I think 10x is the most I need. The more power you get, the more shaky the image. Objective lens size I know is what determines how much light gets in so I'm pretty set on 50mm.