Bessa - rangefinder newbie help

I am about to purchase a Bessa R, after long investigation in the
field, and hearing nothing but praise on that camera.
To spend a little less money, I was thinking about a couple of used
objectives I can buy: a Jupiter-8 50/2, and a Steinheil Orthostigmat
35/4.5

First of all, what do you think of them?

But the question that worries me more - I'm a newbie to rangefinders -
is: any 39mm thread objective is OK? Am I sure that the focusing is
performed without trouble, or have I to recalibrate the rangefinder?


Thanks for your help...

  Alessandro Magni