Most often, the timing,length, etc. of breaks should be determined by the venue and the audience.... if you are playing 'background' for a dining situation, you can pretty much time your breaks as you want ... if you are playing for a dancing crowd, then it depends on what the crowd is doing ... If the dance floor is full, I don't want to take a break, ... on the other hand, if you have played & sung uptempo dance tunes for 45 minutes, YOU might NEED a break ...
I usually find myself not thinking about taking a break, because I am enjoying what I am doing - playing and singing - ...
As for music during the break, I like to control that, and will make it as far removed from what I am playing as possible ... often solo guitar or piano recordings, at a low volume ...
t.
PS ... if you are a guest at a function or you are at a club where there is live music, how many of you time the sets and breaks of the entertainment? ... I do it all the time ...
t.