How much code do the "tabs of notebook" share? If they share a lot, perhaps you'd be better off if you put the common routines into one or more modules (so that you can even reuse it in other projects).

If, on the other hand, each tab has completely separate routines, they you'd be well justified in putting each tab into it's own (or more than one) module.

I should warn you, however, that you might find moving the subroutines into modules after the app is more or less working takes (in my experience) much more work than if you did it right (and modular) in the first place. Often, it takes more effort than it would to just rewrite the thing from scratch.