Buff,
my very first coat is a primer coat, usually sprayed from a can (I use acrylic automotive primer). My base colour is normally either a Humbrol or Revell enamel, normally airbrushed, although in some cases, I'll use brushes instead. With this combo, I have no fear of any reactions between the paints.
Next come the watercolors for washes, which will not damage the enamels nor the acrylic primer. The oils I use for drybrushing and some weathering rust in particular) are applied in tiny amounts, without any additional thinner so they do not do much damage at all, if any (when you let the base coat dry really well) to the enamel base.
However, this technique could easily be followed by replacing the enamel base coat by acrylic (Tamiya, Gunze,..). I, personally, prefer enamels.