Welcome. I've been watching this guy's videos a lot lately, and he walks you through the step by step process of doing astro work with just a camera, lens, and tripod. He has some fantastic results.
Nebula Photos - YouTube
For a camera, I don't recall him saying removing the IR filter is required, and I don't think his regular DSLR has been modified. He also covers how to use multiple programs to process the images. What makes Pentax stand out is the Astrotracer function, which shifts the sensor to follow the stars for much longer exposures without getting star trails. This requires a camera body with GPS built in (I.e. The K1 line or K3 II), or purchasing the Pentax hotshoe mounted stand alone GPS unit for other cameras.
If you want the best single shot image, then one of the K1 full frame bodies would be best, due to high ISO noise handling. If you plan to stack images like in the Nebula Photos videos, then noise isn't much of an issue. In that case, I would consider the K3 II (not the original, which doesn't have GPS) if you want an all in one solution, or the KP plus the GPS unit if you want brand new and the budget allows. The APS-C sensor size will give you 1.5x extra reach for deep sky work. A 300mm lens on that would be like a 450mm lens on a full frame camera.
I personally bought the K3 II in part to do astro work. It's relatively new to me and haven't tried it myself, but the sample photos I've seen from it by others have been astounding.