It is useless to try and fill every pixel on every monitor made. Video has standards and so does compression for frame rate and frame size. Unless you really know exactly what you're doing you should not be using any "custom" composition settings or frame sizes. Your 4K TV may be 4K or it may be slightly larger or slightly smaller. You'll have to check the specifications of yourself. I've already stated the obvious. MPEG H.264 compression (MP4) is the gold standard right now and the frame sizes and frame rates are fixed. Pick a standard and use that for your project. I would also strongly recommend that you do not go above 29.97 frames per second.
I've talked on a chat with Adobe on this issue
and his answer was:
choose maximum bit rate
H.264 would be fine as you looking to play it on a TV
what do you think?
What did you end up doing? Did these settings serve you well? Please let us know.