Whichever one you plan to go to, you can organise taxis quite easily; Silver Top will pick you up, 131 008 is their #.
If your staying in the CBD, there is also the option of a tram from EN (a longer walk, a bus and a train from MB). I dont know any specific details of either sorry.
Moorabbin or Essendon, its really up to you. The only concern you might have is finding the inbound reporting points for either place- an option is to get an airways clearance with vectors to an inbound reporting point.
The Vis Flight Guide on the Casa site (linked in a previous post) from memory has photos of the points; print them out and hand them to your passengers and ask them to look for it too!
MB is cheaper for landing and presumably parking.
EN is probably easier to find your way taxying for parking, however both ground services will help you if you "request detailed taxi instructions". Be very careful with taxying across an active without a clearance at MB due to parallel rwy ops (during twr hrs).
ML Radar (135.70) will help you out with finding inbound reporting points. They do get quite busy and might put you on the backburner, but make sure you contact them if need be and tell them that your unfamilliar with the area and request a vector to whichever reporting point; they will almost certainly always help you out.
DiVosh has already put some great info up.
Ask away if theres anything else