Lots to chew over here. I take the point about Wills being forced into this, and also recognise that instrumentals require different treatment. Keep it varied in as many ways as possible seems to be the thing.
   I have learned, too, how easy it is to confuse songs that are too similar if following one from another. A phenomenon I have noticed is that if you are at a session and an unaccompanied singer follows a singer with backing, they very often start up in the key of the previous song.