If you have DJs, Entertainers, or other staff that you need to add to your projects, the best thing to do would be to add them as 'Service' in your inventory.
From your dashboard, select the "Inventory" tab.
Head to the "Services" tab on the left side of the screen.
Add a new service and fill out the details (including pricing structure) and mark "track conflicts on this service" so you can track for any overbookings (by adding their quantity posted as 1),
Note: If you need your team to access your projects, you'll want to add them as Unlimited Read Only Users or assign them to the project as a Full or Limited User.