You've gotten a lot of good advice already, especially from Graham.
Here's my basic mix for skin. I'm using Reaper Master Series paints, though these colors are similar to what's in your Scale75 set so I'm sure you can get great results with those paints. I like to start with some reddish browns for my shadows, get a dark pink skin for my midtone, and then go into the paler tones for the highlights. I've moved away from using the reddish browns in their pure form, at most I'm doing 80% reddish brown and 20% rosy shadow. And, as Graham mentioned, nice thin layers to build those transitions.
I've been using this general mix (with minor changes) for quite a while. It works well for fairer skin types, northern European, etc. Recently I've gone further by added some red, blue, and purple glazes on top of the basic skin tones. This is especially helpful on faces. Some very thin red glazes in the cheeks, tip of the nose, and bottom of the ear brings more life to the face. A thin blue glaze on the lower half of the face can create the look of stubble. I also like to use a purple glaze to deepen some of the shadows in the cheeks and around the eyes. I'll use similar colors on the body (red on the knuckles, elbows, etc, purple or blue in select shadow areas). Play around and see what you like. Remember to keep these glazes thin. I apply 2 or 3 layers before I start to notice a change. Also, when applying thin glazes, the direction of your brush stroke matters. There will be more paint left where you stop your stroke, so think of it as pushing the color towards where you want it to be.
Here's my basic process on a 54mm face (I use the same approach on 75, 90mm figures and 150-200mm busts). I start out with a base coat of Rosy Shadow, then sketch in the shadows. I add the eyes and then start blending my skin shadows into the midtone and move on to the highlights. The final row of pictures is where I add the glazes. You can see that the 2nd to last row looks fine, but the addition of the glazes makes it look more realistic.
I've put together some tutorials on painting skin and faces that may interest you.
http://powellminipainting.blogspot.com/p/painting-skin-tones.html
http://powellminipainting.blogspot.com/p/painting-faces-step-by-step.html
Again, although I do share my mixes, I think the paints you've got are fine. Just add in a few colors to what you've already got for the final glazing. Hope that helps!