I find most of the Model Color range too thick and clunky to paint straight out of the bottle. It does require thinning. Generally, if I am brush-painting with ModelColor, I will airbrush a primer coat of flat Tamiya acrylic first.
For general coverage, I think a "milk-like" consistency is probably too thin, though you can apply multiple coats (after drying), generally without fear of the paint lifting the previous coat.
There are some fairly detailed tutorials here: http://www.acrylicosvallejo.com/blog/category/model-color/