Number two is the best and simplest cure for the problems other than the hardness and tannins. Maintenance is what it is.
You would backwash the carbon about every 4-5 days an the chlorine in the water would not harm your septic system. The volume of water wouldn't harm a septic system that is working properly now. The filter and softener would rarely do their thing on the same night and you'd program them so there is an hour or more between their using water the same night.