>The question is if every subscription offered on the platform for every space and group has to also be set up as a product within a stripe account, either ours or the creators account.

Yes, if you have the subscription then it is necessary to create the product in the Stripe's side which should be connected with the product / serivce in UNA. If you don't like this way for your customers and you need to get the instant fee instead of sending invoices later, then Credits are the only way to do that.