The right way to use custom Tor Bridges with Multiple Whonix-Gateways?


As far as I understand, Whonix wiki article (Tor Entry Guards) recommends to use one guard per application and use persistent entry guards at the same time, which confuses me.

For example, we have 5 different Qubes-Whonix-Gateways for different identities, all of them are using Tor Bridges. Should we have 5 different bridges or 1 for all for better security? If we choose to manually set them, how often we should change them? Tor Entry Guards Whonix wiki article recommends to rotate bridges every 3.5 months.