Thanks Hooovahh and rolfk for your answers.
Summarized in terms of my questions:
Concerning Question 1: I don't need to close the references, but I may - closing static refnums is in fact a NoOp function
Concerning Question 2: It will always work, because the acquired refnums point to child elements of the FP and are therefore static refnums. See answer to Question 1.
Correct?