-Let's say I put the rangefinder at its minimal focusing distance, using very large aperture(such as F2). From where till where is in focus? Front element till focused distance? 1/3 front, 2/3 back from focused distance?
This depends largely on the focal length of the lens you're using.
For e.g. if you use an ultrawide, a larger/longer depth will be in focus.
In the case of a tele lens, the depth will be much reduced.
Yes, by reading up on the hyperfocal concept you'll be able to understand this more easily