Hardware I/O is covered in the product comparison chart, you just have to scroll down to find it. Your original question asked about how many hardware audio I/O channels are supported in Prime. The answer is in the product comparison chart under Hardware I/O support. Prime supports 2 inputs and 2 outputs while Artist and Pro are unlimited.
Buses are a different concept than audio I/O in Studio One. Buses are software-based routing. It's my understanding is that Prime does not have buses or VCA channels.