The problem I have is that it occassionally gets stuck in one of the inner while loops (requiring a Ctrol-C from me). I'm not sure why. Anyway, the new approach I am outlining here is an attempt to make the program more robust.

How about you make your program more robust by finding the bug? I can't imagine what makes you think that adding more while loops will prevent an infinite loop.

Please don't take code that I've given you, c&p mangle it, then post to ask how to make it work in a new question. It works by not mangling it in the first place.