Wi-Fi MIMO requires the use of two Wi-Fi antennas, hence 2 antennas is the minimum.

If the application the IF573 is used in demands the use of Bluetooth as well a third antenna is required.

For performance reasons the Bluetooth part of the IF573 has its own antenna.

Yes, the Sona-IF573 supports Virtual Simultaneous Dual Band (VSDB) operation.

In an AP and STAion (APSTA) kind of application it is necessary to bring up up the access point (AP) in one band before connecting as a STAtion in the other band.

No, the traditional btattach implementation for BT serial interfaces that relies on vendor specific modules in the kernel is not sufficient because it has no mechanism to incorporate BT_REG_ON/W_DISABLE2# control.

Yes, it's mandatory to enable CTS/RTS in UART, otherwise BT firmware won't be loaded.

Transition mode is to support WPA2 and WPA3 at the same time. In 6GHz band, WPA2 is no longer supported, but just WPA3, and no support of transition mode as well.

According to WI-Fi alliance, only H2E mode is supported in WPA3. It's no longer possible to use HNP (hunt/peck).