So we're dealing with multiple problems here. The gurgling and your talking about air in the system sounded like a head gasket problem and could still be that.
The leak and noise is obviously a different problem. You need to pull the belt so you can spin all the accessories to see what is loose or worn out. You've already found the water pump to be a probable culprit, but don't forget to spin everything while the belt is off. It is a good habit to spin all pulleys even if the belt is just being changed as preventive maintenance.
You'll know more once you've pulled the belt.