The 'disconnect' for a sub panel is the circuit breaker/fuses at the source of the feeder for said sub panel.
You must not exceed six (6) switches at the service entrance (excluding exemptions) ie: a 'main' panel with six (6) switches/brkrs for the feeders/circuits sourced within that panel.
Yes, you can have a 'main' within (or adjacent) to the sub panel, but it is not required.
