Please go on Quintum web and find how they handling 3+ GWs using GK.
However, GK will present himself to peering partner(s), so you will offer only one IP address to outside world. GK will handle traffic, protocols, codecs and send traffic to other GWs. Depending on GK and his features (this is also related to price), you will have more or less function and user frendly interface.
Try to go on openh323.org and find free GK.