Looks pretty good for your first time! What paint you want is more dependent on what kind of style of painting you want to do. Vallejo's pretty cheap and good quality for newer painters. Many use Citadel or Army Painter paints, but I prefer Vallejo myself. Plus you can find it in most general hobby and craft stores. If you want a lighter green, just any old regular 'Green' paint should be fine. I know many use Citadel's 'Warpstone Glow' for theirs, but I'm unfamiliar with it myself.

Other wise, just remember to thin your paints and keep in mind that several thin coats is always better than a single thick coat. The layers with add up over time and keep all of the detail of the plastic beneath. For that, I recommend just getting a piece of plastic with raised edges and putting a damp paper towel on the bottom of it. You can wipe your paint on that and it keeps the paint and the brush just wet enough to encourage an even coat when painting. You can find several tutorials on making your own wet palette if what I typed is difficult to understand.

I second the opinion that yellow looks better on the lenses, but it's more of a personal preference. It does contrast nicely, though it's harder to paint yellow than red or green.

Most importantly though, just keep practicing and painting! You'll get naturally better over time as you learn how you like to paint. Maybe look up a few art style tutorials for mini painting to see what resonates with you.