No doubt, you have asked these questions but they come to mind.
Have you gotten county approval NOT to have a septic system?
Have you planned for placement of the well vis-avis the septic system?
Have you asked the well digger to quote for winter drilling?(I know they can drill thru rock over here so frozen ground is likely doable but the cost increases. Oh, and wells always cost MORE than the estimate, in my experience.Something always 'comes up'!)
Are you going to want to deal with gray water, really?
Building projects test one's mettle!! Good luck.