The GWB does not have a database of it’s own. It is stateless. If you are referring to the MQTT broker, you can easily have multiple GWBs pointed at the same broker. So no you do not need multiple of anything else to have multiple GWBs, just spin up multiple instances and you should be good to go. This would be a similar architecture to if you had a gateway bridge installed on each of your gateways.
Although to be clear the data wouldn’t end up in different topics based on what GWB it uses. The MQTT topic is based off the region and the gateway EUI.
If you are curious about more high-availability / redundancy measures I made a write-up on my own implementation I am currently working on (although I have my GWBs installed on the gateways):