USB OTG, some questions
The situation you're describing is not true OTG. True OTG is when you connect two OTG devices together and they negotiate which one becomes the host. But OTG controllers do allow switching between host and device modes at run-time, so you're on the right track. An OTG host will work normally with non-OTG devices.

8mA is the minimum current that an OTG host must support on VBus. I don't see 5000 mA in the OTG spec tables. Are you sure you're not looking at battery charging? Regardless, you should check the specs for the Bluetooth device to see what current it needs, then design to meet that.