I'd say dont do any layering and stick with the standard naming convention of "stacks". Start with a common stack with all your common stuff and application stacks with stuff that specific to some application say all the resources for a microservice or everything for a BI system ...etc.

Avoid splitting this up as it introduces too much complexity. The IAC code should be very simple such that any dev can pick it up just coming off the tutorials.

Company I'm in has 3 layers and dozens of stacks and it's made the whole thing impossible to reason about. No one wants to touch it anymore which means we now have a Platform team that screws around with this chap for months on end.

Note: Lee Briggs works for Pulumi as a Principal Platform engineer so its in their interest to make this too complicated.