Bill, you can use either 20 or 15 amp breaker, just be sure to use 12GA wire in your new dedicated circuit. Most electricians will use 14ga wire for a 15 amp circuit.
One other thing to mention too. Before you plug the breaker into the panel, look and see which side or leg your kitchen frige is on, and select the other side or phase. no point of going to all that work then pulling power off the same leg your fridge is on, introducing the motor noise into your gear.
You may also want to look into a dedicated ground, which will remove additional noise, but just make sure you issolate the ground from the rest of your house.
You also did not mention how hold your house is, but many homes built in the 80s used the outlets where the wire can be pushed in from the back. Don't use those. Make sure the screw terminals are used so you get a solid connection.
best