I have been using oil paints for figure-painting for a long time an there are a number of things to consider.
First: oils tend to need a relatively long period to dry completely - this is heavily dependant on layer thickness (the thicker the layer, the longer the drying time) and colour (some colours are more 'oily' than others). Many of my figures are dry to the touch after one or two days of drying (I am using a drying chamber and paint in very thin layers - as in paint a layer, then using a dry brush remove as much of the paint as possible) so I can paint another layer on top, but that does not mean that the oil is completely dry - which means It may not be wise to 'seal' it in by means of varnish as the oil cannot evaporate anymore and stays within the paint layer.
Second: the student version of any brand usually has fewer pigments (that which provides the colour) and a much higher percentage of carrier (in this case natural oil as in plant oil). It is possible to remove as much of the oil as possible by letting it 'leak out' as follows: place a small amount of oil on a piece of cardboard (any cardboard will do, I use pizza boxes - the ones that are frozen, not the ones that come from a pizza delivery company such as Pizza Hut - but cereal boxes will do just as well). Leaving the paint on that surface for at least 15 minutes before using it. - but the longer you leave it, the less oil will be in the paint, the more difficult it will be to paint surfaces as the paint will not 'flow' from your brush.
I have used mostly Winsor and Thalens as brands, and have found that colours such as lamp black, titanium white, raw umber, raw sienna, burnt umber and burnt sienna have a low percentage of oil compared with for instance 'Prussian Blue' (very oily stuff, dries with a sheen if not used with care). To use as a wash on plastic kits (non-figures) I mix the oil paint with turpentine substitute (cheaper than the real artist turpentine, which I use for my figures). I do not think this is a major issue with the washes, but for historical subjects in my figure painting I try not to dilute my oils at all, as they tend to show some erratic behaviour - mostly altering the exact colour shade I am after, or drying with a sheen where without thinner I have a completely matt finish.
Hope this helps.