If the Time Capsule is set up in Bridge Mode, which Apple calls "Off (Bridge Mode)", then it does not matter whether the Ethernet cable connects to the WAN "O" port, or to one of the three <--> LAN Ethernet ports, because all ports behave the same.....as LAN ports.....in Bridge Mode. Makes sense to use the WAN port though to keep things simple.
Is this the best configuration ?
Opinions vary. Some users would advise connecting an Ethernet switch to the Starlink Router and then connecting other Ethernet devices to the switch. The main reason for this is troubleshooting potential issues in the future.
If you connect the Time Capsule directly to the Starlink Router and then connect other Ethernet devices to the Time Capsule.......and the Time Capsule has a network problem........then all of the other devices connected to the Time Capsule will also likely have a problem.
If you connect an Ethernet switch to the Starlink Router and then connect other Ethernet devices to the switch, the Time Capsule might have a problem, but other devices will not be affected.
Should Time Capsule be first in line ?
Your decision, keeping in mind the information just above.