Can I have both a CSP Azure Plan and a separate pay-as-you-go Azure subscription?

Yes, technically a tenant can have multiple Azure subscriptions of different types simultaneously — for example, an Azure Plan managed through a CSP partner alongside a separate Pay-As-You-Go subscription billed directly to Microsoft, perhaps for a different team or project.

This does mean separate invoices for each billing relationship and separate access/cost management to track, so most organizations consolidate under one model unless there's a specific reason (like a legacy subscription being harder to migrate) to keep them split.