Also should this be done before or after the face is shaded and highlighted.
This bit first, I usually glaze the red mixture I'm using on top of the fully-shaded skin.
I'm some what of a beginner using acrylics but I also have oil paints.
It's possible to do the effect equally well in either medium but since you have oils I would recommend you use them for this kind of thing (over either a
completely dry oil paintjob or the face done in acrylics).
Oil paints are much better suited to glazing because of their slow drying and the medium is much more forgiving if you make a mistake since you can easily wipe the colour off the surface with a spirit-dampened brush and then start again. If you do something similar with acrylics you're generally going to need to repaint that area to a degree.
Don't want to get it too pinkish...
Don't use pink then
You can sometimes get away with using neat red for this sort of effect on the cheeks - don't forget the chin, nose and ears as well, which are often affected too - but occasionally you'll want to tone it down somewhat, so you'll need to add in a little mixing complement (and then a touch of white, since the mix will go darker) or alternatively mix in a little grey of around the same value as the red.
Any advise or tips would be greatly appreciated...
With oils you can put a dot of the paint onto the surface and then just work it in with a clean brush, using a gentle back-and-forth action and/or by stippling towards the edges, which can neatly give a fade from a red 'hotspot' out to the normal skin colour.
If you go with the acrylics you would generally apply the paint very thinly in successive layers to build up to the final colour. This is easy enough on smaller-scale pieces but it's quite challenging at larger sizes.
Oh and don't forget to paint the underlying skin paler than you would normally.
Einion