IBC VFC 15-150 Modulating boiler with 10:1 ratio

I'm looking to install an IBC VFC 15-150 in my 5500 sq ft home in Long Island. Heat loss comes in at 90K for the home. However, with 6+ members drawing down an indirect HW tank (120 gal or so) for showering I feel that the added capacity of the VFC will help keep up with the HW demand and the 10:1 modulation will still allow for efficient heating.

Any thoughts?

Also, considering the water quality issues in Long Island, am I better of with a SS tank or perhaps a stone lined or even glass lined tank?

Suggestions welcome.