I think the "one-size-fits-all" medium format system is an illusion. There won't be one system that does all you want (there almost never is). If you try and go that route by choosing the most buildable and adaptable system, you'll end up with a system that does nothing you want
properly.
In the end you might end up with some interchangeable-lens, slow-photography system like a Rollei SL66 or a RB67 or a Technika for portrait and landscape work, and something more hands-on like a Rolleicord or a Mamiya 6 or a folder for street and carry-around photography.
The biggest problem I think is finding something that suits
you, as opposed something suggested to you by people because it suits
them. Expect to dabble in different systems for a while until you've found the thing for you. This may actually be quite difficult for you, seeing that you are far away from places where you can take a look at the medium format gear used by other photographers. I would dread a situation where I have to buy things like medium format photo gear with no chance of trying it out beforehand for at least a week or two with a loaner.
If you want something cheap and you really are in Kokchetau and you get to Almaty or even Astana at least every now and then, you could just hang around on local Kazakh user forums like
Tsentr Tyazhesti (which has a fairly good
photo section with classifieds). See if you find a photographer who sells you, for example, a working Iskra, or a Kiev 60 with, say, a 150/f2.8 Kaleinar and a good wideangle. Your chances in getting a good one are a lot higher than in the West, because people will have been using the camera themselves and you can talk to them. (I just bought an Iskra and a couple of Zenits from the Kyrgyz equivalent,
Diesel Forum). Don't get involved in the Soviet systems too far, but for portraiture and landscapes, for example, it might be an easier start than a Technika 70, at least if you're in Kazakhstan. At least you can actually get the gear and try it yourself and find a repairman if you need one, which is worth more than having a supposedly-reputable system that you have to buy when on a short trip to the West and that will fail on you as soon as you're back, BTDT.)