> As a side note, I find it helpful to think of what the high level business objects will be at the beginning, but build a bunch of utility functions from the bottom up

Yeah I think this is a reasonable approach, especially as if you do end up completing this, and get to a design you are happy with, it will probably be very different (and hopefully infinitely superior) to your original high level design.

You've probably already heard of it but the mikado method can also be useful in some of these situations.