You sound to be in a similar situation like I was in 2012 when I bought a second hand MFD Linhof Techno system.
My Linhof Techno review could be helpful to you (which talk about tech cams in more generic terms too not only the Techno):
http://www.ludd.ltu.se/~torger/photography/linhof-techno-review.htmlIf you get into MF with the right expectations it can be wonderful, but don't buy too much into the hype. Much of the hype is about studio work, out of focus look and skin tones, something you have little use of in landscape. In landscape much of the hype is related to the resolving power of the most expensive tech cam lenses on the highest resolution backs, something you and I doesn't afford.
That said, if you want a DSLR experience there's the 645Z, there you have the CMOS technology and all features you find in a 135 DSLR, and for being MF it's affordable and there's still a few second hand lenses to be had.
I think it was very worthwhile to go the tech cam way, but then you need to compromise a bit concerning digital back. You can get a Hasselblad CFV-50c with CMOS and liveview, buying it in Japan it's $10k, but wide angles will be an issue as documented elsewhere. If you shoot wide angle it's better with a CCD. P45+ is popular due to its well-documented reliability and long exposure, but is also one of the most expensive second hand backs. I got myself a Leaf Aptus 75 and still today it's very good price/performance (for being MFD), and you can do focus check unlike on the P45+ (most older backs render 100% view so fuzzy you can't know for sure it's sharp or not).
Compared to a D810 you will miss mainly a few things with the CCD backs, 1) they're more noisy, 2) you don't have (any good/usable) live view, 3) most don't have long exposure. Using grad filters is a good idea, and having a post-processing style that's not too much grunge HDR-like, ie don't push shadows 4 stops. If you have a bit more old-school processing you'll find also the older CCD backs to have good DR, a back from 2004 still has better DR than a recent Canon, and noise is well-behaved no patterns and such. Concerning long exposure there are a few exceptions like the P25+ and P45+, but most are limited to about 30 seconds, and at 30 seconds they're quite noisy if the weather is warm. I use my Aptus 75 up to its 30 second limit quite often but shoot often in cold weather too.
Concerning lacking the live view there are two methods, A) ground glass, B) high precision focusing rings on the pancake cameras. In my review I look into ground glass focusing extensively, and yes with training, the right gear (glass and loupe) and not shooting wider than f/11 you will achieve good precision with ground glass.
I recommend a view camera solution like the Linhof Techno I have myself (best landscape camera much thanks to it's compactness, but also rather expensive, but if you find one second hand it can be okay), or Arca-Swiss MF-two or F-Universalis. The Cambo Actus is not so good choice unless you get a CMOS back as the Actus lacks sliding back option. Why do I recommend a view camera? You get about the same type of creative options concerning lens movements as traditional large format, lenses are a lot cheaper as you get them on lens boards, and you have tilt and swing on *all* lenses as it's built into the camera body not an expensive mount. The disadvantages is ground glass focusing and somewhat lower precision (due to more flexible movements), I don't think view cameras should be shot at wider apertures than f/11 as shorter depth of fields both make ground glass focusing overly difficult and also can make precision limitations in the systems visible.
Note that ground glass focusing is not for everyone, if you have problems with your vision it may be impossible to get the good precision I talk about. If that's the case a pancake camera with high precision focusing rings and a laser distance meter can be better. If you're all about sharpness and less about movements a pancake camera is probably also a better choice. You won't get bad sharpness with a view camera but focusing precision is a bit more, well, relaxed.
I think the best way to approach tech cam landscape photography is to think that you want to shoot large format but not mess with film, then you will be most pleased with what you get from a Linhof Techno or similar camera with a second hand back at 33-39 megapixels.
If you're only into MF for image quality and think the rest is just cumbersome and a bit too costly I think you will not be in for long. We've not seen the end of quality improvements of the 135 systems. What you won't get though is the same type of flexibility concerning movements at such wide range of focal lengths as you can get in a tech cam. If you become a bit romantic about old-school mechanical things (like I do) you will also get some extra joy out of the precision mechanical instruments tech cams are. That helps.
I've also noted that there are different type of personalities when it comes to MFD. You have the engineering type like myself that don't see MFD as something inherently special and superior but rather look at the technical aspects of image quality and says it is what it is, which is that it's worse in many aspects than the best CMOS sensors. Then you have those that see special properties in the format size and the fact that it's a CCD and very much dislike anything that looks "DSLR-like", I'm not going to say that it's not real, but I and many others don't have eyes for that and don't see it. How you are in that regard will also affect how pleased you will be with MFD. That said I am very pleased with my MFD despite that I find a little bit better image quality in a D810 in some aspects, so it depends on what your expectations are too. I think that there is such a thing as "good enough" image quality, and if you aim there you don't need to pay a fortune for you digital back. If dynamic range is one of your primary concerns when you make your pictures then there's a warning sign to be raised, you probably won't be pleased with anything but CMOS, and then Pentax 645Z is a good choice, you won't get movements though.
You won't get the same reach as your 200mm F/4 though. The longest lens you can get in the digital lens range is 210mm, which is a bit hard to get now since it's been discontinued due to low sales. If you compromise quality a bit you can get some analog tele lenses which are a bit longer. My longest is 180mm, which corresponds to about 135mm on full-frame 135. So if very long lenses is central to your creative photography tech cam can disappoint.
Do make sure that you have your image clear on the wide angle end before you invest. It's there you have the compatibility issues and potential very high costs buried. SK28 and SK35 is very good price/performance and movement flexibility compared to alternatives, but when shifted only play well with larger pixel sensors (39 or less) and the Kodak 50 megapixel sensor found only in Hasseblad backs. Otherwise you need the more expensive Rodenstock Digaron lenses on the wide end.