You have some beautiful craftsmanship in those handrails and the window frames look so crisply cut - no wobbly knife marks in the corners! Humbrol paints, hmmm, not as good as they used to be a few years ago. They have changed their formulation due to health and safety and although the paints look okay in the tin, they seem to be lacking pigment and come out more transluscent rather than a solid colour. I've found it makes no difference whether you spray them with an airbrush or apply with a paint brush, they lack colour 'depth', especially in the lighter shades. I have a yellow anchor roller on my build, it has had 11 spray coats of humbrol and the grey undercoat still shows through.