I could be wrong, but I assume he is laying down his main coat (Black) with spray to a disassembled body, and then assembles and adds some of the custom parts, and hand paints the parts that were already attached to the body when it was sprayed, then attached the layers of the car with wheels last in final assembly. That's how I would do it, and will be doing it. Hand paint in layers, starting with darker versions of the colours you want and adding small amounts of a lighter version of the colour as you work up or out, which gives the object a more real and deep appearance (highlighting) If you want to add weathering, try some dry brushing techniques to give worn, weathered, and dirty appearances to the surface of items, or even washes for some various looks of the recessed details.
Spray with a nice flat, non glossy protective clear coat to protect your work, with final assembly of the layers, (windows and seats) with the wheels dead last, depending on hard it is to hold the car while painting the details. Even for this, I would prefer to grab one of the rivet pins of the shell with a small vice grip, or clamp or fingers and have it held that way while you devil up the details with the fine brush. If clear coating, I would protect the wheels and windows from this spray if already fully assembled.
There are more than one way to get all this done, but this is the mode I will be attempting with my first builds of the Interceptor. I'm still in the sculpting stage of the front end and spoilers, and looking to get 'er down to a science, or even a basic mould, then the brushes come out of retirement.
