Maybe I have missed something by why didnt you just buy a Sky Q box off the bay. They will still work with all the free channels just fine, you just loose the ability to pause, rewind and record.
When I ditched Sky I tried playing with the Freesat thing built my old TV (LG Oled) and it didn't work for the reasons listed here. I looked at getting a Freesat box but they all looked naff, I liked the SKY Q ui so gave up messing around and just bought a second hand Sky Q box (cost me £30).
I got a new TV recently (Sony Bravia 9) and tried seeing it Freesat would work on that with the Sky Q LNB and it does. It found so many dupes of channels though and the UI was horrible. I was hoping to ditch a box and a remote but nope, back to using the Sky Q box.