1. You can have one dish on a motor (positioner) which moves it back and forth to aim at different satellites. The dish can be large or small.
You can also have one fixed dish which does not move and has multiple gizmos on the front of the dish (LNB's they are called). These would point at different satellites.
2. Pretty much, you have paid satellite with its own dish and receiver and then FTA satellite with its separate dish and its own receiver. The systems are different and don't mix. There is another paid satellite TV called 4DTV with which you can mix FTA. (Search google.com for 4DTV.)
3a. I don't think you could receive anything through new energy saving glass. Might be able to if old regular glass or plastic glass.
3b. For paid TV, look at other peoples dishes and see what direction they are pointing. This would be the direction you would need for paid TV. For FTA, there are satellites almost anywhere in the sky which have FTA on them. But the satellites you would receive from your limited view may not be what you want. Satellite locations along with channels are at lyngsat.com, use a dish pointing calculator and compass to find the direction each satellite is at from your location.
First, I would call your local paid satellite provider and have them come out to your apartment. See if they can install a dish inside which would work or not. They should be able to tell you.
FTA takes a lot of reading to learn about. Read and study all the following to learn about all this...
Satellites and channels...
lyngsat.com
Satellite location finder...
http://www.geosatfinder.com
All about FTA, dishes, and satellites...
http://www.geo-orbit.org/sizepgs/tuningp2.html
Search google.com for words you do not understand.