You probably already know this, but just in case, make sure you get off the bus at Kidani Village and not Jambo House for Sanaa. I've stayed at both, and every single bus ride someone gets off at the wrong one. There's a shuttle you can take between the two that picks up right in front of each building in case you want to visit Jambo House, too.
Buses from MK to AKL are usually pretty full in my experience, and the ride takes about 20 min. I've been on many standing room only busses to and from MK from AKL - just make sure you're prepared and give yourself plenty of time.
Have fun and enjoy! Sanaa is one of my very favorite restaurants on property.