I also prefer the gym area to be seperate from the HT area same as sir Cardo. Kapag kasi may ibang gamit sa theater room parang cluttered ang dating especially if you have the bulky gym equipment in the background. Just use your old CRT TV for the gym room para makatagal ka ng exercise. Pero kung no choice talaga, oks lang na magkasama yung HT and gym, ang mahalaga kasi eh yung may pinapanood ka sa tv habang nageexercise. For my wife, I just bought a seperate 20" panny flat panel lcd para kung gusto niyang dalhin sa gym or kitchen area habang nagluluto, masya pa rin siya.
Yung tungkol sa mga socket, kung sa akin lang tama na 1 on each wall. If you can buy something like the monster power center or anything similar, this will help protect your investment. It acts as a surge protector and eliminates signal polluting noise, tapos marami siyang saksakan.
This is the 1 I bought. simple yet effective.
front view:

rear:

Maganda rin kung naka wall mount ang surround speakers mo as opposed to using speakerstands for the rear speakers. Mas maganda kasi tunog pag nakataas yung rear speakers at hindi ear level while iin your seat.
If your planning to add some bass shakers for your theater seats, this is where the socket on the rear wall comes in. The bass shakers really pack a punch especially when viewing action pack movies.

The general rule daw according to 1 of the electronic stores I've been in regarding viewing distance is that there should be a 6:1 ratio, that is for every 6 diagonal inch of your tv, there should be a foot of distance from the tv to your seat. So if your going to buy a 50 inch tv, your viewing distance should be atleast 8 feet of distance from the tv to your chair. For CRT's it should be furtheraway.
You should also invest in good cables like yung "monster cables" to maximize the capabilities of your HDTV.Those stock cables just wont do if your watching HD movies.