You couldn’t just use water and water-mixable paints for the whole of the course. You would have to add a linseed oil or a medium that contains oil. You would then have to use a thinner for diluting/cleaning brushes. If you added a water-mixable medium (that contains oil) or a linseed oil you could adapt the mixes. You would then have to use a thinner for diluting/cleaning brushes.
This is from Cobra paints:
“The first layer must be applied lean. For this, the paint is thinned with water. During the drying of this layer no compact film of paint is formed, but rather a porous one. Oil from a following layer will, therefore, be absorbed by the underlying lean layer and so when drying will adhere within the numerous pores. This helps to create good adhesion between these two layers. As an underlying (lean) layer abstracts oil from the top layer, it has to be ensured during painting that the underlying layer has relatively more oil. If this is not the case this will affect the quality of the painting.
As of this point, there are various possibilities for continuing further:
Thin each subsequent layer with increasingly less water; each subsequent layer, therefore, contains relatively more oil. You can eventually end up with pure paint.
Thin the paint for the following layer with painting medium.”