https://en.m.wikipedia.org/wiki/Lime_mortar
If its line mortar replace it with lime mortar otherwise you will have a foundation failure down the line. The lime mortar is a sacrificial material. If you use normal cement, moisture will instead pass through the rocks and eventually those will fail. Old houses are all about sacrificing materials to maintain the bones of the house.
I already live where I want to live. I would probably buy up all the open land in my county. Get my friends to move out and live on one of my properties. Fix up this 120 year old farm house. Install a pond and more water features to hold onto rain water. Probably run some electric fencing get solar power go off grid. Pretend to be a cattle rancher. Try to turn this homestead into my very own paradise. But i’ll probably employ a-lot of people create some jobs do more charity work.