Water chemistry can be a big topic to dive into...but "high in calcium" is seldom a big problem for brewing water (unless all you brew are pale lagers). Often it is the bicarbonate that may come along with the calcium that is an issue. Using spring water is not a bad way to go if you don't know what is in your tap water.I always use spring water from the store, the water here is high in calcium.
As far as this topic, I tend to think that the cooler based mashtuns were great when that was about the only option. These days, either single vessel BIAB or the single vessel all-in-one systems are the best systems for making typical 5 gallon (or smaller) batches. I used to brew 3-vessel fly sparge, but moved to BIAB 3-4 years ago.