Maybe you're thinking about things too much!

Each platform is going to have its advantages and disadvantages, and I'd take that article with a grain of salt - he can be a little hyperbolic sometimes! When he mentions difficulty in focusing an SLR, he's referring to the fact that SLRs typically focus using the widest aperture, regardless of the aperture you've selected to capture your image. For example, if your lens' widest aperture is f/2 and the aperture ring is on f/8, it's going to use f/2 to focus. This means that the plane of focus is will be smaller than a lens with a widest aperture of f/4. With a smaller focal plane, or in other words, a more shallow depth of field, you need to be more precise where you place your focus since you don't have as much room for error. On the flip side, with a shallow depth of field, you know exactly what's in focus and what isn't. Maybe check out a camera with an included depth of field preview that will stop down the lens so you can see in real time what will be in focus in the final image. I found that when I was first starting out this helped me immensely.

With that being said, I really wouldn't worry too much about mirror or focus screen adjustments unless you find that the camera you ultimately pick up needs it. Of all the SLRs I've used, none of them have needed adjustment and it isn't that common compared to rangefinders requiring re-calibration every now and then. I shoot with my Nikon F2 (which I would highly recommend) from 1977 multiple times a week and it works flawlessly.

When it comes to rangefinders, there's no sense of depth of field because you aren't looking through the lens. The depth of field will only be apparent when viewing the final image. This simplifies focusing because the rangefinder patch is all you need to worry about, regardless of the aperture you're using or the widest aperture of your lens.

In summary, it sounds like you need an SLR for the kind of photography you're into. People have been using SLRs for decades and decades. They aren't "bad" or "inaccurate" or difficult to use. I switched from a RF to an SLR and am loving it so much. Also, there's absolutely nothing wrong with manual focus lenses - many many people are using them to this day with no issues whatsoever. Just don't think about it too much, do some research for which body you think will best suit you and go from there!