If you have already started painting, then this might not help, but i would stick to a white under coat as you achieve a much better depth of colour
IMO, and keep to greens that take washes well, and of course, keep your paint thin, don't paint straight out the tub. The
GW foundation paints are a good place to start as they seem to take washes well and give a good coat in thin layers.
Here is a pic of a pilot i'm doing in greens to give you an idea of what im on about.
Once the washes are done, all the details are reviled and easy to pic out, and gives you i guide for you highlighting. To keep the mini 'together'
i try and have one highlighting colour mixer, normally an off white/brown/grey, this provides a good set of highlight that don't over contrast.
For details, colours that contrast well will keep you mini looking more "real' but it depends what look your going for, as for basing, i agree with 'the green god'. But have to thought about some small leaves on the ground, you could make then from thin plasti card?
Hope that helps.