Re: working on new HT now; couple of questions...
Well, first off, the subwoofer placement is something you have to try and see, no one can tell you where it will work, and the two spots you might 'pick' might not be best.... so this will be a challenge until you hook it up and see what works.
As for running the cable box and DVD 35 feet away from your rack, I wouldn't. You will need long cable runs that could be avoided by using a good RF remote (I prefer the Harmony 890 which is ~$289 @ Amazon) that way all the gear can be out of sight, and be controlled easily. This will mean you'd need to go to the other side of the room to put a DVD in, but that is a minor thing, and one only done at most every two hours, so should be tolerated even by the most demanding of wives. With a good remote, the cable box can be controlled form 100 feet or more away without a line of sight.
You will definitely want an HDMI cable to the TV, but depending on what you have/buy, you might also need component if you receiver or pre/pro doesn't transcode video to HDMI, if it does/will, then HDMI will be fine. 35' isn't outside the realm of HDMI, I have a friend who uses a 50' Monoprice for his projector and it works well, and Monoprice is the cheapest HDMI cable I know of.
Do you need a 20A dedicated line for a subwoofer?? Probably not, but I like the way you think, I DO have dedicated lines for my subs, but I am not the norm.
Ken Taraszka, MD