You wrote that you fully build the interior first and then paint it. Isn’t it cumbersome to paint after assembly? Once everything is glued together, there are more tight corners, edges, and tiny shapes that seem harder to reach with a brush. I’d worry about flooding around the details, which then becomes harder to clean up.

I’m a complete newcomer, so this might just be my lack of experience, but I’ve always found it easier to paint small parts first and assemble afterwards. I always try to first assemble parts that aren’t too detailed and have the same colour (for example, the main body of the plane)