My apologies - very late! I thought I had answered this question some time back but perhaps not. And I'm sure it's too late now!

But for he record, usually when doing this sort of work, we start with selecting several samples of trim within the style range we are looking for. We then just play with them - seeing what looks best together and at what spacing. This can also be done by drawing it out to scale but sometimes it's just easier to do it on site and create the look you want.