a) with the excellent Focus Peaking I can use FINALLY existing old Leica R lenses useful. The focus has hitherto also placed halfway sharply with any other camera, which immediately leads to the incredible resolution and depth of field to committee (of course you can also dim, but the bokeh makes precisely the difference). The speed during the manual focus rises practically to the old Leica feeling!
The same should also apply to anyone who has still lying around good old lenses useless that there mW for most systems suitable adapters, and as required, it can certainly be the A7 or A7R.
b) is a must for me on several occasions. However, the image quality seems to suffer significantly (to be tested in more detail below), so to use rather for documentary purposes.
c) Of course. With 12 MP also useful: up to very high ISO areas good results (not just photo studio quality, but completely usable for private purposes, and patches of color are no longer as annoying as in previous generations of cameras).
When using E-mount lenses that have been counted for APS-C (eg. NEX-series), the resolution drops to about 5 MP. Can you use therefore, reserves have been then but no longer. Sony full-frame lenses I have not tried it yet.
Small drawback: the battery runs down pretty quickly pulled; So always think of Reserve; possibly power saving function to shortest interval? A rough estimate: for private purposes per scheduled hour photo session (camera on) take 1 Battery. For videos, I would rather calculate 1/2 hour per battery.
