I would set up your configuration as follows...
Node and File Share Majority quorum model
Node 1, Node 2 and file share witness at primary dc
Node 3 at DR dc
1 vote to each node in the primary data center & fileshare witness
0 vote to node in the DR data center
preferred owners node 1 & node 2
AG synchronous mode between node 1 & 2 automatic failover
AG asynchronous mode to node 3 manual failover
primary AG on node 1 with readable secondary replicas at node 2. Since you plan to use readable secondary replica, you will have to license node 2 as well as node 1. Node 3 will be covered by software assurance. I assume this is a production environment.