In terms of HDMI cables cutting out I’ll be surprised if it’s the quality of the cable, that distance isn’t excessive.
I tend to use pretty cheap ones and haven’t had such an issue.
With regards to a PC again you don’t need to go mad. It’s mostly about the graphics card.
The itself can be 4th gen i3 and above with 8mb RAM. Make sure you get an WAS rather than a traditional hard drive, the speed difference is remarkable.
Graphics card needs to be a GTX 960 or above.
This will be the expensive part.
Dave has some fantastic guides which he’ll hook you up with and offers the best advice on this subject bar none.
He’ll tailor your tv with the most appropriate setup.