Home Theater:

Screen:
The size of the picture is important only in that it can fill the proper "look angle" from the viewer's seats. A 19" tube is perfectly acceptable in a small apartment space. A 60" screen will strain the viewer's peripheral vision, just as sitting in the front row of a theater would not be pleasant after the first few days.
Seating:
Your theater must be able to seat each viewer comfortably. All viewers must have an adequate perspective on the screen. Here are some examples to think about: A ratio of about 3:1 is about right - this translates to putting your eyes about 5 feet away from your 19" TV. A 2: 1 ratio is OK for immersing yourself into a movie, but it's a bit close for Tom Brokaw. And 5:1 is the outer limit - after that, you will find yourself leaning forward to see the details. As for seating off the center line, about half the distance to the screen is about it. So for seating spread, that's 5 feet of couch space for your 19" set.
Sound:
The sound image should be centered around the screen. Additional equipment would be placed and positioned to add depth of sound. 
Lighting:
The management of ambient light can enhance your theatrical experience. Remember, too much light will wash your images out, too little will have you stumbling in the dark. Try to find a happy medium that's right for your room. 
Control:
One key to taking full advantage of each aspect of your Home Theater is to be able to control it simply. One small set of buttons should turn it on , change modes, channels & volume, and shut it down.