I have two metal buildings that we use as a workshop and storage.
In the future, I want to make one of them a bunkhouse.
My idea is to frame the interior walls with wood 2" x 4", add insulation, and then use either sheetrock or paneling.
The paneling has gotten hard to find so I would probably end up with sheet rock.
Will you be turning the building into living quarters?
Since you mentioned cof, a rocket mass heater might be something nice to plan for:
https://permies.com/w/cob-style-rmh