We have the same situation: New house on well and septic system. Water is quite hard and has a lot of fine sediment in it.
We put in Two (in parallel) whole-house Culligan water filters (the kind you can get at Home Depot). One will restrict the water flow too much - you need two in parallel.
We followed that with a water softener. We use potassium chloride instead of sodium chloride salt. I know there's no definitive studies but we use the potassium 1) for health, 2) for the septic system and 3) for the house plants.
I ran a separate water supply from BEFORE the filters to the hose bibbs on the outside of the house. No use watering the lawn with filtered and softened water.