180K input tankless works fine in coldwater states, as long as you don't need to run two showers simultaneously with other loads in the middle of winter. I lived for years with a 125K unit in Worcester MA, with midwinter incoming water temps in the high 40s. I'm now heatin my house & hot water with a single 180K tankless, but with a 48 gallon buffer tank with internal heat exchanger. I can run a single shower all day long with a full heat load and it keeps up, but with 2 it would fall short when the heating is running.
A water softener is advisable, but annual descaling would still keep up at 5-10 grains hardness.