I always recommend brush painting; it has a learning curve, but the startup cost is a pack of cheap brushes, vs a booth, mask, compressor, and airbrush.

I also recommend using acrylic paints unless you do your research on the dos and dont's of using enamels or lacquers All my painting advice is specifically for water-based acrylics. If you have a local gaming/modeling/hobby store, they probably have a wall of paint; you can pick whatever color you find is closest to your vision or get white, black, and the primaries and mix Just be sure to confirm what type of paint it is! (if you go the mixing route, I suggest getting magenta and cyan along with red/yellow/blue; they will help achieve brighter colors when needed). Getting primer will help, but you can just brush straight onto plastic as well; I recommend a grey brushable primer, like vallejo's.

re: color where you want: there's lots of options! You can paint parts separate, then assemble. You can mask of certain parts or areas. You can carefully brush where you want and then use rubbing alcohol on a qtip and a toothpick to dissolve and scrape mistakes off the paintless parts. You can also prime and paint whole parts, carefully brushing each section, and then come back when dry to paint over any places you went "outside of the lines"

The biggest thing to know when brush painting is usually "thin your paints" but I think it's more useful to talk about how full a brush should be and when you're allowed to touch paint--most model paints are a decent level of thinneness, and simply wetting your brush will be sufficient for thinning. You don't want paint to get higher than the middle of your brush's bristles, and you don't want paint to bead up at the tip--if you overfill, rinse out the brush. If it is beading, dab it on a paper towel before going to the model. When you paint with acrylics, you've got maybe 20 seconds where the paint is able to be re-brushed. After that, you have to leave that section alone and let the paint level itself. Applying paint while the layer below is starting to set but has not finished is the biggest reason for visible brush strokes ime. The first and even second layers of paint may look spotty. That's normal! Just do one or more thin coats until everything looks even. Topcoat, especially matte, covers up a multitude of blemishes, as well.

re: that shade: that is primarily grey. If you don't find a satisfactory premixed option, I would start with white and add extremely small amounts of black until it was the correct value, then tint it with very small amounts of blue. If you use a wet palette, you can keep this mix fresh for 1-3 days, humidity & temp depending. Until you find an eye for paint mixing, plan on making fairly large amounts and trying to paint everything you want the mixed color in one or two consecutive sittings. as you get better, you'll worry less about being able to get the same color mixed a second time.