I have an off the wall question, for me it's off the wall for my lack of paint experence...
Is it possable to mix Model Masters enamals with Winston/Newton oil paint..... The reason I ask is that they both can be thinned with mineral spirits fairly well... I've not tryed this it is more one of "THE THINGS THAT MAKE YOU GO....HUMMMM?""

ANY KIND OF PAINT EXPERIENCE WILL HELP...

I mix humbrol enamels and oils all the time. Great when figure painting as it gives more drying time and allows you to work it better. I also blend them for washes, as the oils have a fine pigment and dont dry too quick allowing you to clean up runs.
I would be 99.9% sure your OK to go with what you suggested. Dont think the water soluable W&N would be good though.

Yep, I mix them regularly wiith never a problem.

I've never tried Model Master enamels , but I use mixtures of Humbrol matt enamels with oil paints a lot on figures. It gives longer drying times than enamel with the blending ability of oils. Using matt enamels in the mix helps to flatten the finish and the mixture dries faster than oils alone.