I sense a disconnect, or perhaps an overload is a better way to say it, around the word “role”. There may not be a 1:1 – or even a clear – relation between the roles your individual hosts play in your infrastructure and the Ansible roles you need or want to run against those hosts. This is a very hand-wavy answer, but a lot depends on what you actually have in your Satellite/Foreman and CMDB that you could draw on to inform other processes. Plus, you mentioned you’re migrating from Saltstack; I imagine that your Saltstack way of organizing things is going to influence the approach you take in Ansible. And that’s okay!
Trust your instincts. You have a better feel for your environment than we do, and there are lots of legitimate ways to do things. Build it in a way you’re comfortable maintaining it. And if you have second thoughts later on, embrace change and refactor early and often.