JeffCapnfpv The controller will support SBUS on UART #2, so yes the R-XSR is an excellent choice.

JeffCapnfpv The controller chip itself has the UARTs available but they are not available on any solder pads. If you have the ability to do very detailed soldering, you can solder directly to the STM32 legs and then Betaflight will support external rx. I have done many this way, but I wouldn't recommend it to people who aren't capable of such fine soldering.

JeffCapnfpv Look here on BG for just plain 5V buzzer. The large ones are probably self powered with battery backup, not really needed for whoop sized drones.