I'm not sure what your last question is about.
MOst acrylics don't work well as washes, their pigment is too course and water alone has too much surface tension.
I put a dab of oil paint on a palette, much like this month's article suggests, the add thinner until it flows freeely with capillary action. I place a small amount where I want it, at panel lines. at the base of raise detail, etc. Adding very little at a time eliminates the need to wipe off excess. I find that too risky to paint and decals. I also don;t wash aircraft, since IMHO, the ocer-accented panel lines this produces gives a very unrealistic appearance.
When using enamels, I used the same general technique.
If you allow your paint to dry thooughroughly and use this method, you should be able to apply an eanmel/oil wash over acrylics as well as enamels.