Best way to structure code for combining continuous pin watch with repeating function?

I'm not sure I can be much help either, except to say that IMO it's a good idea to re-use as much code as possible. If you've got a function you're using in both places, definitely keep that.

Also, for anything more than a few lines it's worth using a named function rather than just inserting it into a setWatch/setInterval. eg.:

//Use:

function onSecond() {
...};
setInterval(onSecond, 1000);

//rather than:

setInterval(function() {
...}, 1000);

As it allows you toreplace the function in running code if you're developing and want to tweak something.

But I'm not convinced that really answers your question :)