Hi Andrei,
welcome to the Carl Zeiss world!
As with most CZ lenses, these are a great coupling (shows you how non-discriminating I am).
My only reservations against the 85mm f2.8 is the 85mm f1.4 and the likelihood that you'll acquire one as long as you stay in the Contax/CZ tradition.
I use a 135mm f2.8 MM and a 85mm f1.4 AE for projecting slides mostly. I didn't go for the 85mm f2.8 years ago; instead I saved up for a extra year to make up forthe f1.4 I'm not convinced by the portability argument; at least er, not until I saw a beautiful silver 45mm Tessar...) Carrying an extra 300grams on a camera body has never been absolutely critical for me; I'd rather shave the weight off myself than my camera, or carry a lighter tripod head and bag.
The 85mm f2.8 is light - here in the UK, it was marketed as a mountaineering lens (lightweight and portable). It is more flexible and easier to operate (a bit like a standard lens) than the 135mm lens.
The 135mm lens is not particularly large (only around 9-10cm long) however has a longer focus travel (not ideal for panning, candids and grab shots). It weighs around 565g, which balances beautifully with your 167MT too. At f5.6 onwards it is pristine and sharp (beware of camerashake at this focal length, especially handheld). You might not be able to handhold that, particularly given its extra focal length. If you don't carry a tripod regularly, consider that as a rationale for opting for the 85mm f2.8 which is easier to handhold without shake, and hence more flexible.
Since you are now in the Carl Zeiss system, do you envisage never ever owning a 85mm f1.4 lens? I can't say how much I love this lens; in its German incarnation, I consider it the most perfect lens in my collection; yes, its large in diameter, weighs exactly the same as the 135mm f2.8, however you have a four-fold gain in speed. Yes, it vignettes with Cokin A filters when a 67-62mm step-down ring is used (you might want to find out if that's true for the 85mm f2.8 if you use squares). The 135mm does not have a problem with the Cokin A system even wide-open.
Consider whether the depth of focus is shallow enough at f2.8 for portraiture; I enjoy the extreme Victorian out-of-focus experience which I get with a wide-open 85mm f1.4. You just don't get that with a 85mm f2.8. With the 135mm's extra compression in perspective and the shallower depth of focus, it's not a problem.
Considering your enquiry about differences in AE and MM versions of the CZ lenses, I do believe Michael has given a few comments about this.
Any difference is beyond me at projection level; I've resigned myself to believing that anyone who can ascertain any fine tuned discrepancies in either contrast or resolution between AE and MM lenses may have a third eyeball somewhere.
Perhaps as the AE lenses are older, subjected to fungi attacks, and mould on the coatings in humid countries and many more years of abuse by previous owners. Get a MM new one if you can afford it then.
You might want to consider the minimum focusing distance; the 135mm is around 1.6metres, which may put you off if you do portraiture or studio work, or get you up against a wall in order to fill the frame. It is a moderate telephoto and I quite love the perspective it gives, for landscapes anyway. However the pincushion distortion might be a little more evident than on 85mm f2.8 or f1.4 (which is just not noticeable to me). I don't find the 135mm as contrasty as the 85mm either.
The 85mm lens has a minimum focus distance or around 1metre - that's quite invaluable for a portrait lens if you're using it for portraits.
Should I throw another spanner in the works by mentioning the 28mm-85mm zoom; for the sake of f0.5 - is it really worthwhile having a prime 85mm, when such a beautiful zoom exists?
Best wishes in your hunt for perspective.
Joe99