I want to connect my computer to my DVDR (and thus my tv's) but for now,
I'm no longer interested in Roku or any of the other services. I just
want to sit in bed or a more comforable chair to watch a free Youtube or
Hulu video. And for now I'm not going to worry about wireless.
Also, my largest TV is 19 inches and at least 10 years old so I'm not
needing... . whatever one needs to have a big picture (what is that?)

They're a little under 50 feet apart.

First, if I get a 50' active (amplified) USB cable, will it actually
work for my USB keyboard/mouse (that I to buy still.)? 50 feet is not
too far? I thought I'd get a wireless one and plug the dongle into
the 50' foot extension cable. Is that okay?

Second, I have two choices for the audio-video. For audio, in either
case, I will use the output from the sound car with a stereo Y-connector
to split for the local speakers and the remote TV, and a different kind
of Y connector to split to left and right RCA connectors. (Unless there
is good, cheap way to transmit both left and right on the same cable??)

So with all that, the choices are
1) two 50' RCA cables and one 50' S-Video cable. versus
2) one 50' Cat6 cable with an AV balun at each end. (one with jacks for
S-video and L and R audio.)

Which will work better? What will be bad about the other one? ;-) .

Is 50 feet too far for either to work nicely?

(HDMI and optical are not possible, because of available outputs and
inputs.)

Same questions if the cables are 100' long instead of 50'? Because of
the next paragraph.

They're a little under 50 feet apart and I'd like to hide the wires. if
I were to run the wires into the wall, up to the attic, over to the
rear, down to the closet, along the baseboard, etc. it woudl take 100
feet. Were I to buy 100 foot wires now and leave 50 feet
of them coiled at one end or the other, could that cause interference or
choking or any problem with S-Video, RCA cables, Cat 5e or Cat 6?

Should I use Cat6 even if it's a little more expensive than Cat5e?

Thanks for any heop you can give.