I am using a custom made paint that has a similar colour to the original DeAgostini parts.

You will find that the colour of the insigni White will change with the different layers of weathering you do. As for the sheen you can like you said use a Matt coat, My choice of Matt coat of this scale is Humbrols rattle can Acrylic Matt (49) applied in light coats

I'd wait, paint in the different colored panels and tick marks (they are all over if you look), do a gloss coat then apply decals (they have said we're getting decals, of what I do not know. The display they were showing had the 5 foot model decals on it, maybe we'll get those. The 32" model didn't have any decals applied, though everyone who worked on the model signed their name all over in various places, maybe we're getting decals of their signatures to match the studio model?). After decals, seal them with another gloss coat, then start weathering. If you do a wash with thinned down paint you can keep it in the recesses and edges with a gloss coat, a dull coat will tint the whole area darker. I assume he'll cover washes and other weathering techniques in his videos

A point about colors, he correctly states that lighting conditions affect how the paint looks and various TV and monitors are all set differently so you can't really go by what you see in one picture to the next. Then he talked about using color chips to determine pantone color codes off the studio model to paint his own model. The model he took those colors off is not the same model that was used for filming, well physically it was, but what he had access to had sat in a warehouse for 25 years, with yellowing paint, accumulated dirt and grime, had people smoking around it, and was generally beat up; not the new freshly painted and built model that was filmed.

I am using it and like the look.