A dead flat finish with no brush strokes can be achieved if one uses the right tools and products.
What I have shown here would be unconventioal products normally not associated with modeling however they work great and IMO are much better than any modeling paint on the market.
The paint has a very good open time, Meaning: It stays wet long enough for the paint to flow out thus eliminating brush marks. They are highly pigmented and cover fantastic. Once they start to dry they dry to the touch in about 1-3 hours and are very hard and durable when letting dry over nght.
The One Shot brand was he gold standard when Sign Artists would actually swing a brush for signage. They cover well. Dry hard and are very durable.
The next would be the brushes. The two shown are called lettering Quills and come in various sizes and types of hairs. The hairs are Russian Squirrel Hair and are very soft.... the one on the left is a brown hair and the one on the right is a grey. The brown is the softer of the two.
I hope you find this helpful, I know this combinaton will give you great results.