I've used both Floquil and acrylics (usually "craft paints") in a variety
of colors (but always some shade of brown/tuscan/mineral red) and
apply them with a brush. I do the 'details' such as door hardware,
brake wheels, etc. at the same time and I don't pay much attention
to 'coverage' ... just to whether or not I am getting any paint on the
body of the car. I use a shade that is 'slightly different' from the
body color of the car to make the details so highlighted "pop" out
from the body/field color of the car ... when I say "pop" I am talking
about "just enough difference (subtle) that the detail part/coupler/
whatever separates itself from the body". This adds a sort of
"depth" to the overall look of the car.
I also add a fairly heavy coat of grime to the underside of the
car and lesser amount to the roof. Dust/grime along the lower
part of the sides is something I do "sometimes but not always".
Typically, I do the details before my final application of some
sort of VERY light "blending color" ... this can be grime, dust,
dull coat, weathered black, etc. and is very lightly applied so
that unless you look for it you don't notice it.
I pay attention to each car "one at a time" in order to get them
to "look all the same when a yard is looked at from a distance -
but if you focus on the individual cars in a cut they aren't all the
same. One of the keys to that is to mix up a unique batch of
weathering colors for each weathering session and even vary
them during the session (especially in how much is applied to
The end result is a car that looks right (to -my- eye). Your
methods may be different - these are mine.