Scott in VA wrote:
I thought I could do the same in reverse for the showers, replacing the 70 gallon tank with a 40 gallon tank, then installing 120v tankless in each bathroom in case the water runs cold.
Larry is giving great advice. Reduce the load and do the math.
Once the “water runs cold” won’t the tankless have to heat the incoming water to the desired setpoint all by itself? Is the unit capable of doing that? If it is, why have the tank?
Don’t disregard the maintenance aspect of any tankless/tank for a long and happy life.