GOP by customer priority - Quantity based allocation not percentage

We have requirement as below. Can anyone suggest using Post ATP hook vs customized allocation without enabling Allocated ATP.

- Few priority customers - can setup priority by demand class

- Users can maintain inventory in priority subinventory / any other logical bucket

- GOP should suggest non priority customers only the inventory which is in non-priority buckets (subinventories)

- GOP should suggest priority customers both priority inventory and non priority inventory

- Plan should consider priority inventory segregated to priority customers.

Environment:

- ATP based on Planned output

- Separate instances

- 24 X 7 ATP

- Not using Allocated ATP due to GOP considering allocation for entire horizon (need priority by request date)