ANT and Bluetooth are communication protocols that behave differently and serve different purposes. ANT simply broadcasts information for anyone to listen to, so you can pair 10 bike computers to the same power meter over ANT at the same time. Bluetooth uses an actual connection between 2 devices which allows it to change communication parameters constantly and perform better in noisy environments. For this reason, you can only pair one bluetooth device to the power meter bluetooth connection at one time.

You can, however, still use ANT while the Bluetooth connection is occupied. 

TLDR: As many as you want to ANT. Only one for Bluetooth. Can do both simultaneously.