yup
I believe the 6 stage is for water supplies with high TDS and uses the extra unit upfront to extend the DI filter's life span.
BRS using filters that remove chloramine. If your supply uses this, and not simple chorine, make sure your filter will remove it (not all do)
Water pressure is important. You need sufficient water pressure for units to work properly and more is usually better, but too much can't break the unit. Make sure you have sufficient pressure. (i think most units require 40psi). 60 psi is the standard the industry uses to measure efficiency - it's just the amount they use to compare models since pressure affect efficiency
water reports are easy to obtain and usually available online.
75 gallons per day seems to be the default rate, but other speeds are available if you need to make more. 50 gpd will leave you waiting longer, so don't bother.