1) Yes always more or less the same people and no, draw manipulation doesn't work because there are not many inactive teams. (It stops working well at level 40 to 50 in my experience)
This means it works a bit. You don't get abandoned teams as opponents, but if you have a weak team yourself you tend to get the weakest possible opposition in league. There is only 1 CL and cup for every around 3 levels though, so you can't manipulate this much in these 2 competitions.
2) On my server the top plays the same level every 3 seasons. So 2 season the top also gets promoted and then 1 season there are maybe not enough players, thats why they are forced to tank so that others can catch up.
3) It is very different from server to server. I know one server, where a friend plays, where there are several 150+% teams (mostly still due to friendly bug) and servers there are only 1 or 2 teams in that region. But top of the server is generally the place where all the good players meet.
4) They have to be, if they not finish top 8 they will eventually fall off top server and need 3 more seasons to catch them again. So activity is very high in high levels, especially top of the server.
5) If both are my friend, I support no one.
But I don't add this many friends ingame.