It seems the most straight forward way would be to buy a Mac Mini and attached it to the TV. Is that not an option?
To get the upstairs Mac attached to the TV, you might take a look at HDMI over ethernet solutions, although I don't know if they will work with a Mac. That would let you use standard network cable to run the HDMI signal over longer distances.
If that were to work, then it would just be a Mac control problem with there are several options. Do you have an iPhone or iPad? You could set up a free Logmein account and use their free app
to access the Mac remotely. There is also Mobile Mouse
which allows you to use your iOS device as a track pad for your computer which might also be useful depending on your final set up.
As far as I'm concerned, it's a damned shame that a field as potentially dynamic and vital as journalism should be overrun with dullards, bums, and hacks, hag-ridden with myopia, apathy, and complacence, and generally stuck in a bog of stagnant mediocrity. - Hunter S. Thompson, 1958, from cover letter he wrote for a newspaper job.