Congratulations on your purchase. :^)) The grass and road tiles are excellent, very nice color choices.

Your trees lack a nice dark color to give them a healthy range of contrast. You need a dark green or purple to add some extra depth to the darks. Also, if you are devoting such a huge portion of the objects into that purple, you might add a lighter shade of purple or two to give them more detail. That, or make the reflected light more subtle.

Regardless, this is some top notch stuff.

Ah, I dig. Yeah, there are books that teach the fundamentals and inner workings of machines, rotary parts, and the like. Probably the best place to look is in the engineering section of a college bookstore. They won't be aimed at artists, but there should be enough diagrams and illustrations to get some use out of them. Seems like they'd be pretty expensive though. There's always used bookstores, I've found tons of valuable reference material sifting through bargain bins.

Now all she needs is a kinky house wife outfit. :^))

Love what you've done with the face. I'd say brighten up the whites of her eyes and darken her mouth, they are getting lost in the face and making it look too blurry. Her hair could also do with some smoother AA on her left / our right.

Right now, the tree is the character. There's no reason this can't work without some mammal hogging up all the space.

This can be quite moody if you add some drama to the shading. The moon and clouds have a high contrast foreboding quality to them, but then the landscape below gets all gray and, well, meh. Darken the shadows on the near side of the tree, and add some specs to the far side from the moon light. Maybe put some rim light on the underside of the trunk. Also, I think the piece will be stronger if the bottom and top corners go dark. A dark mountainous forest silhouetted by the clouds individual treetops drawn out by the moon light.

The moon bugs me, the ring of light around it seems unnecessary. The actual moon is nice and rounded, but the ring around it is more hexagonal than circular. Also the rings look pillowy, not anti-aliased.

This scene looks like an underwater adventure. There is WAY too much blue in every shade, and not nearly enough saturation. Perhaps you have some issues with your monitor calibration?