absolutely not oil. It takes forever to dry, and its translucency may make it difficult to get the desired results. I would also stay away from using any extra dryers, or thinners with acrylic (besides water) Acrylic drys to a plastic sheen in a few minutes. You can use a hair dryer to speed up the drying. Use a water spray bottle to keep the paint wet every 30 seconds or so, if your job will take some time.
I personally prefer the more opaque acrylics. Sometimes their are numbers on the tube stating the opaqueness.
If you have a lot of touchup on a multicolored piece, I would recommend getting several colors. The most difficult to get right and not too dark are the purples and cool blues.
Lead or Cadmium White
Black
Cadmium Red
Ultramarine Blue (cool)
Cerulean Blue (warm)
Cadmium Yellow
You might also want some form of premixed violet, green, and orange. You may want a cool yellow, and cool red as well as the colors listed above to properly mix clean colors. Mixing a cool blue with a warm red will muddy your colors. Mixing a touch of white in with the cool colors may help reduce their translucency.
That's all general info. It varies greatly from manufacturer to manufacturer.