Agreed with all of that though automatic audio calibration features of most receivers takes care of wire length issues (not that humans could really tell the difference) and some placement issues.
I would look into Atmos speaker systems (or add-ons) as well if you have a flat ceiling you can bounce sound off (or can put actual height speakers up). It can be a notable upgrade for any UHD with a dynamic soundtrack.
Your best place to ask about specific equipment or combinations is going to be on avsforum, especially since it sounds like you are using your PC as the media source. The HTPC forum will address a lot of possible issues around possible image and sound considerations/concerns/limitations (like there is no UHD Blu-ray player or software yet).