Water Tank Setup - 1-Tank System vs. 2-Tank System vs Tankless

[Furnace]

Hello,
I did a quick search on this topic but could not find any relevant results, so I've posted a new topic.

We are building our home right now and need to decide on what type of hot water heating system we will be using.

House Details:
4 Full Baths (including master with 55 Gallon tub and separate shower)
1 Dishwasher
1 Laundry Washer
12 Hot Water Taps at Sink Locations

There are only two of us in the house now, but expectation is there to be 3 or 4 in the near future.

From my understanding my options are (Gas Heaters):
1.) 75 Gallon Tank set at lowest heat setting
2.) Two smaller tanks run in series with each other. First one set at lowest setting, Second one set at desired hot water temperature.
3.) Tankless system.

When I brought up the Tankless system with my plumber, he said that the maximum load requirement of the home will likely be two high for one Tankless system. We would likely need two tankless heaters. Also, we have very hard water here in Edmonton, Alberta and the tankless system would need constant maintenance.

My main questions are, will there be a big difference in running costs between option 1 and 2? Also, I've heard that running option 2 should give me more hot water then option 1?

Any advice would be much appreciated.

Thanks!

[hj]

Option #2 would depend on the size of the two tanks, but I would operate them both at the same temperature in order to get the maximum volume from them. Essentially, you only heat the water you use, excluding standby heat loss, so the operating costs would be about the same for #1 and #2, but the total gallonage of #2 would determine how much greater its capacity would be than the 75 gallon heater. In most cases you can buy two 50 gallon heaters for the same, or less, than one 75 gallon heater.