I've recently asked about recursive workflow use that @kent used and he said
However, I also just realized you asked about the physical cost.... not the resource cost.
as for your other questions, in my opinion these boil down to 1 main question:
- do you want to retrieve and process on the server side or the client (browser) side?
workflows would be server side, functions will be client (not counting functions in workflows lol).
you could split it, load pages from a workflow then return the data to the page and process it there.... or you could do it the other way around, normally you want the connections to databases on the server where it's safer, but since we're using Retool that's not too big of an issue here so you'll probably want the more process/time intensive on the server side.