The critical item determining if your cost for NEMA 14-50 is a few hundred or well perhaps over $2,000 is what is the service to your house - by that I mean the physical size of the wires and the amp capacity of your circuit breaker box. If your house is only 100 amp (possible given the age, but i doubt it), you will have at a minimum replace your current breaker box and possibly get larger wires from the utility pole to your house. In some locations, the utility upgrades these wires and in others the home owner does. A call to your electric company might tell you what the amp capacity to your house is - this is the wire size item, not the capacity of the breaker box. It is not uncommon for the utility to run larger/oversized wires to a house just so if people upgrade the utility does not have to redo the wires from the street. Knowing your address and when the house was built are questions they may ask.
Your voltage is nominally 240/220 if you have 3 wires going from the pole to your house.
Higher voltage and higher amps not only charge faster, there is also less wasted electricity. No electrical process is 100% efficient. So just in terms of electricity costs, if I charge my Tesla on 120 volts I will have to use more electricity than if I use the 240 volt NEMA 14-50 system.
Dual and single chargers affect the maximum charging speed when connected to an AC electrical outlet (your garage, a hotel electrical line, etc.). It will have no effect on the Supercharger usage - that said if you get the MS with the 60Kwh battery, you have to pay for Supercharger capability.
One thing going on that I don't see a lot of mention in these forums is a program between Tesla and destinations. Tesla is offering free equipment and paying half the wiring costs, as I understand it, to places like hotels and resorts. These facilities then offer fast charging (something called HPWC) can be very fast. Dual chargers are needed to make the HPWC as faster than a NEMA 14-50 system. When I am 500 or a 1,000 miles from home I would much rather be able to charge at 58 miles per hour of charging than only 29. That won't happen every week, but it will happen often enough that I ordered dual chargers.
People talk about 50 and 40 amp NEMA 14-50 charging capacities. The proper wiring will be a 50 amp breaker and #6 wire rated at 55 amps. The Tesla itself only allows drawing 80% of the max amp capacity. So a 50 amp system will only charge at a 40 amp rate. Same thing applies to a 15 amp 120 volt wall plug - it will charge at only 12 amps.
Spend some time reading in this forum and at Charger and Range section of
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