Hi Lindsey
On question 1. Both methods you describe are valid, but the Z value might need to be larger depending on your vertical tolerance. As to which is better, that is up the each consumer. Personally, I like the transformer tanks spread out so I can see each one. But, I could see where having them stack might better for spatial placement, you just have to remember to set the Z value or set it in the template.
As for Question #2, I would use a Electric Assembly/Low Voltage Service and then place all my services as content of the assembly and then use a Line End on the Low Voltage line and create connectivity associations from the Low Voltage Services (meters) to the line end. When multiple ElectricDevices and ElectircJunctions share the same X,Y,Z, only one will get connected to the network. Since only 1 has the same Z as the line, it is the only one connected. Connectivity from coincidence requires the same X,Y,Z and you can only have one Device or Junction as the same X,Y,Z.
John Alsup
jalsup@esri.com