My gas water heater is only 6 months old so I don't want to get rid of it but I need to install an electric water heater to qualify for the "all electric rate" from the utility company.  Since geothermal is providing warm/hot water a good portion of the year I figured if I hook the two together it would give me 90 gallons of water storage and thus take less energy to heat any extra hot water we may need.  Plus I like the idea of having an extra 40 gallons of good drinking water available if needed.

Plumbers:
Is there any drawback to having the water go into the supply line of the gas hot water heater (unhooked from gas) and then feed the operational electric hot water heater?  Does the gas hot water heater need to be a little higher in height when feeding into the hot water heater?  Will the electric w/h get enough "pressurized" water pressure from the other w/h when refilling to keep up with demand?  We don't use a lot of hot water and the biggest draw (other than clothes washer) is just when the wife and I are getting around in the morning for work, daughter takes her shower/bath at night and the niece will only be here for another couple months.  ETA:  The two electric w/h's I was looking at had two different wattage double heating elements (4,500w & 5,500w)...with my setup and needs would the 4,500w heater be enough and the 5,500w just be overkill and just waste more energy?

Sorry if the questions weren't asked very well but I hope you know what I was getting at.  Thanks!

Tankless would be great for a small cabin I hope to build someday in Idaho and Florida but is not feasible for our house as it would take 2 or 3 of them to provide adequate hot water.

One of the side benefits of the geothermal is that it provides hot water for the home for at least 6 months of the year so the water heaters will store that hot water with little to no energy needed to produce hot water.  I just want to make sure this setup will work with the two water heaters hooked together with the geothermal system.

No experience yet as the drilling rig is sitting in the back yard and the geothermal unit is sitting in our garage...should be all up and running on Tuesday weather (rain) permitting.  We presently don't have A/C in our house so the geothermal will be a pleasant surprise when the weather starts to get warm and humid.