Thank you Katja for the suggestion, but I can only get to the guest WC through the current office, right?
In a granny flat, that is the shower-bath, so not your guest WC. Your guest WC would have to be separate. It is difficult to make suggestions for rooms or life planning that you do not mention or mention late. So it should not be a granny flat, but an office. Only in an emergency should someone sleep there if they become in need of care. One would like to know that before making the effort. In #1 it explicitly said a second residential unit for later. You also have not yet said whether you are willing to make compromises with the living spaces? What kind of office is it? Are clients expected there or could it also be accessible via the living space on the south side?
Can you tell me which tool you use to model the rooms?
My program is called Architect 3D. Unfortunately, some important tools are missing or faulty. For example, you cannot draw spiral stairs and the square meter areas are calculated incorrectly.