I want to make a "studio" in my barn that my college age son can stay in independently when he is on breaks and I can work in when he is away. I want to keep it simple and rustic and not invest too much money because 'a second residential" unit is most likely not allowed. I was thinking button up the holes under the floor and around the perimeter fieldstone foundation with cement so that the field mice dont come in, clean- clean- and clean,

The boards are exposed, can I put just the standard pink insulation batts and drywall around the perimeter walls? Do i need some sort of vapor barrier? I havent seen any leaks or obseved any water damage.

Electricity hooked up to the main house but I plan on setting up solar energy.

Plan on getting a Composting toilet.

Have a large woodstove that heats the structure nicely.

There is water running to it already (just a regular water spicket) to water my garden-- and electricity. My biggest concern is the grey water, i would like a small water efficient shower and sink and would like to drain the water into holding tanks and pump/drain into the garden but not sure how to reuse during the winter months. Ive considered also just getting a travel trailer with a hotwater tank for showers/light cooking.

Just hoping others have maybe attempted something like this and can give me feedback regarding the best way to go about it and/or concerns or tips about'what not to do"