I think you should understand about the shadow of the connection with this:
because the shadow shouldn't fall straight below, right?
About those game sprites, those are really cool, i see nothing wrong with anatomy or whatsoever. You might want to use some more contrast on the shades on the sprites, like a little bigger difference between darkgreen and lightgreen. The background seems a little boring though: There's not much detail, especially on the doors. Also the wires/cables are too bright. Other than that, it looks wonderful.
You could make different topics for different pictures, but you could have pictures of the same category in the same topic (ie. if you plan on making more things for that game, you might want a topic about the game). If you plan on making a lot of unrelated pictures though, you can make a big topic for everything you do. Check out the other topics here on the forum, and then decide what would be best for you.