Switching from a SQL Server 2016 Failover Cluster to Availability Groups
Do you need to have the same server configuration for both nodes?


No, this is not required, however it is a best practice. In the event that your secondary replica has fewer cores and less memory then you would see a degradation in performance when failed over to the lower powered machine. This might still give you sufficient performance, only you can make that decision, but it is not a requirement.

One thing I would recommend is to always ensure that you keep the drive letters and paths the same on all machines in an AG, otherwise you'll run into a lot of problems attempting to add data or log files.


  How does Disaster Recovery work?


You will need to license your secondary if you allow read intent routing. That is something that gets configured at the AG level. But ALWAYS check with a licensing representative to ensure that you are compliant.

You should not need additional bandwidth for AG traffic if you are already using mirroring. Packets are compressed prior to sending between machines (when running in asynchronous commit mode).


  Can I create a primary for one AG and a different AG for another?


Yes. 

The limitation here is that a database can only reside within a single AG, and that all nodes must be in the same WSFC. Be aware though (going back to your licensing question) that if a server is a primary for databases then it must be appropriately licensed.