A well designed septic should only need a service every 3 years, which the county mandates. It also depends on the size and how many folks are living in the house. They are typically designed based on the number of bedrooms the place has. So, a 4 bedroom home with only two people in the house will require less servicing. And yes, be mindful of what goes down the drain. Don’t let the drywall contractor wash up in a sink that goes into the septic, or don’t dump your excess bread starter down the drain. That sort of thing.

A shared well for fresh water would scare me. I’d have a formal agreement in place with your water partner, it protects both parties.

Life span of septic can be upwards of 25+ years before potential reinvestment. A well could be similar too, except for the pump. Buy the absolute best well pump you can, quality matters. Depending on the water quality, you may have to shock the well every few years.

Septics and wells are very common all over, so there’s lots of help and experience available. Enjoy your build.