The standby losses of any water heater are dependent on several things: surface area, the differential temperature (water in the tank to the surrounding air), and the quality and quantity of insulation. Electric WH have typically lower standby losses than those with burners, since the burner and flue must be uninsulated. So, from a standby loss, a bigger single tank would be more efficient. Keep in mind that you only heat the water you use, so a bigger tank by itself won't have much more cost unless you draw more water from it and therefore have to heat more - IOW, keeping it hot isn't a big thing, and the standby losses of one big one would be less than two smaller ones.
Shutting off and bypassing a WH can be done, but you'd want to probably drain the tank that was going to be unused for a long period otherwise, you'd end up with stagnant water that would likely grow some nasties in it. ANd, you'd probably want a lock-out on the circuit breaker to prevent someone from turning it on accidentally, since you'd burn out the elements in minutes if there were no water surrounding them.
Having a second WH closer to the point of use will mean hot water faster, so that's a good thing, but the addition of a hot water recirculation system would make it faster still, even from one point.
There are probably other pros and cons, and certainly opinions. See what others have to say. Basically, you can do it either way. You can also make any WH have a larger apparent volume if you raise the storage temperature and use a tempering valve on it's outlet to limit the outlet temperature to a safe value (generally considered to be 120-degrees max for a residence). Say, run the WH at 180 and after mixing, you'd have lots more water at 120 than you would if the tank started out at 120.