Can I replace my oil-based water heater with several electric ones?
You're adding more points of failure, and when the small tank runs out, you will see a temperature drop until the tank fills with hot water from the reserve. You also have to worry about eventually reselling the home. Given that, my preference is to keep it simple with a single tank.

One option to give you the same effect is a single electric tank with the lower element turned down. You are then only keeping half of the tank hot but can easily adjust it to have full capacity.