1. In queue, once a message is read, it will not be sent to another reader. A topic allows you to implement multiple readers that are focused on the same set of messages.
2. No, you have to use at least the Standard tier to use topics.
3. Dead letter queue is used to avoid blocking your queue by an invalid message.
4. In Azure Service Bus, sessions are used to ensure the FIFO message processing.
5. The maximum size of a queue with partitioning is 80 GBs.
6. In the active replication, you are sending a message to both namespaces. In the passive model, you send a message to the secondary namespace, but only if it can be delivered to the primary one.
7. You have to define the primary and secondary regions, pair them, and define a trigger for failover.