I feel the same way you do about Windows, and actually briefly used MediaPortal, it's a decent program but I just REALLY hate having to run Windows for the exact same reasons you gave. I have also tried Mythbuntu but had problems getting it to recognize my DVB-S2 cards, and never could get it to work (YMMV). I've had the best luck with TVHeadEnd running on Ubuntu Server, but then I run a separate backend (it is used ONLY as a backend, not as a frontend and not for any other function besides a satellite TV backend). If I also wanted to run Kodi I'd choose standard Ubuntu. I am still running Ubuntu 14.04; I don't think I'll upgrade to 16.04 until it's been out for a while longer and people aren't reporting problems.
Regarding tuners, there are good ones and cheap ones.
TBS Technologies makes both consumer grade and professional grade cards, and the professional grade ones cost a significant amount more than the consumer grade, but the consumer grade ones work fine for many people. But there is one issue, you need to compile their drivers on your Linux box, and you have to do it again every time you install a Linux kernel update. There is a
bash script that makes that easier. Just recently someone told me that there are now
open source drivers available for some of their cards; previously they were all closed source, but for now I'm personally sticking with the old drivers because I know they work and because the open source ones don't yet support my card. If you are in North America it's a lot easier and less expensive to get the TBS cards than most other brands. I don't disagree that other brands might be better than their consumer grade cards but in North America they are probably cost about the same price as the TBS professional cards or maybe even more, especially if you have to import them from Europe. Since you mentioned CI and CAM I assume you are NOT in North America, since we don't have that stuff here. So, you may have more choices for cards than we do.
Be careful of older cards that don't support newer formats such as 8PSK and 16APSK. 8PSK is widely used now and 16APSK may become more widely used, depending on where you are in the world.
One other thing to be aware of is that not all motherboards play well with satellite cards, so don't buy a new motherboard unless you can exchange it if it doesn't work. And even the ones that do work might have an issue with conflicting interrupts; you can see
this article about that problem (and the fix for TBS cards).