1. You can define as many as targets as you want (each of them is a new exporter) and you can define filter independently.
2. If you want something dynamic it's very easy. As I said, if you configure all your log servers with exporter to the same server you will have all the logs if they are defined properly in SmartConsole. For example, let's say you have a dedicated log server and MGMT - you define exporters for both of them to same server and in SmartConsole you define to the GWs that if the primary log server isn't available, send it to the other.
3. If the server itself went down then I think (not sure 100%) that the exporter doesn't know that the logs aren't received (but maybe this could change between vendors). If you have 2 servers you can export the logs to, this will a proper backup. If this is on Check Point side the exporter will know to continue from the same place AFAIK. There's also a way to export a specific log file so we can always re-send something if we think logs might be missing.
Kind regards, Amir Senn