Multiple Rounds and Group Size - #2

There is an old thread here somewhere that addresses aspects of this question but left some issues unresolved in my mind...  So let me try to get clarification.

First  question: in multi-round tournaments, how are the groups in the 2nd and following rounds determined? Are they 'seeded' by rating in just the same way that the groups are initially formed? 

Second question: what happens if there are 'unfilled' groups? 

For example, let's say group size is 5 and in round one there are eleven groups (for a total of 55 players).  If one player from each group advances to  round two that would be eleven players.  So that would result in two groups of five players and one group of one player???

Can anyone clarify how this works?