I know a lot of people have aftermarket head units that have BT ability, so the caller screen just uses the HU.
Not sure where you could mount an external one that won't be in the way. You could try making a mount that goes in that useless square cup holder that doesnt hold cups under the left vent. The only issue with that is in the winter you'd be blowing heat directly on the thing.
as for the mic, Ive seen it on windsheilds/headliners near the rear view mirror.