Dual mode Bluetooth for transmitting audio and connecting with an App
1) Yes, your BT dongle will require a MCU.

2) Sorry, didn't understand what you meant.

3) Bluetooth allows for communication in both ways, your only stress should be coding the MCU properly for your application.

4) This is a product design question and I definitely couldn't answer... depends on your product goals.

5)  I would say one of your best options is to get a BT device that already comes with MCU. Check out this example part from bluegiga.