These are interiors from other aircraft to consider as patterns.
The airrests, seat spacing and finish, and panel layout provide some insight.
This view give a bit of a pilot picture of floorspace and instrument layout.
Thhough beautifully appointed and finished, the colors are not appealing for me.
The red interior is also not appealing for me, but this picture gives a good idea of the rear seat area.
I am envisioning mahagony siding with lighter colored, button tuck leather seats.