Have you considered an indirect water heater that heats as a separate zone from a gas/oil boiler?
Weil McLain has the gold series
Amtrol makes a good unit and The hottest one on the market now is the Phase 3 which the better plumbing supplies now carry
Having a water heater you know you will have to replace about every 10-12 years plus the dangers of having a “fired pressure vessel” even if it is electric.
These indirect heaters are much more energy efficient with much less stand by losses plus have a very large peek demand capacity.
Why have the extra LARGER tank when this is a safe proven a energy proven system.
Check out your options before investing in HW tank.