To help the OP, let's break down some of the Rolleiflex nomenclature. Using typical US terms and simplifying. Looking at post WWII Rolleiflexes (no 'Cords, no SLRs).
Two major groups based on lenses. Automat: X, MX, and MX-EVS. Tessar or Xenar lens.
The Alphabets?? Letter cameras? C, D, E, and F. lenses can be Planar or Xenotar. Aperture can be 2.8 or 3.5 on the E or F models, 2.8 only on the C and D.
(There are A and B Rolleiflexes but they were small production runs and rarely seen)(rare because they were flawed, not that they are desirable).
Mechanically, ALL of these cameras above are basically the same. The focus system, wind system, aperture and shutter dials, Automat film sensor, etc. You can look at a late 1930s Rolleiflex Automat and a 1970s F and you'd see very similar parts, including some that can be swapped directly. Sure, some mechanisms were improved. And bells and whistles were added. But at core they are the same camera.
Meters: started with the E models. This is an uncoupled meter, and there are many E models without meters. ALL F models have coupled meters (look for the extra dial below and to the back of the focus knob). Both E and F use selenium cell meters, many of which are either not working or not accurate. It's easy to pull the meter block and put a slug in the opening.
Condition is key. And the safest way to get a usable camera is buying from a known seller.
So decide what is acceptable in lens type. Meter? Then start looking.
I'd suggest anyone new to Rolleiflexes avoid buying from Ebay. Far too easy to end up with a problem camera.
