Beyond a welcome I will start of saying that your pixels show a lot of potential and effort and kudos to you for that. I too have probably mentioned your high color count.

1 - aa =hand placed pixels to create the illusion of anti-alias = smoothing the jaggy lines/pixels. This is not always needed but you'll get asked to do some all the time. Its a personal choice. Some go with pixelly pixels, others like to blur the line to a point it may not even be pixelart to the casual viewer. Stake your position but experiment from time to time.
2- dithering is blending two colors to create the illusion of a third. Here you should be aware that the less colors you use the higher the respect you'll get from other pixellers, as a general rule. You should still go for your artistic vision but colors that are so close together that the can be the same is the art of palette unification (your work could use this). The depth/3D/contrast you seek will happen once you refine your color choices from the high counts you are using. Its a process so hang in there. Many ways to dither and checking PJ galleries will reveal all the better/cooler ways (start with hall of fame).
3- I rather like your color choices. Indeed they are a little 'primitive' but the basic good sense is there. One great way to explore this very subjective area is to borrow other's palettes (you MUST give a nod/credit) to the person, k). If you see a pixel where these colors choices you speak of are used, start there and throw a little experimentation in here and there. Don't fear we will let you know if it works ;).
4- don't know what those are :/

Your 'hush' pixel is awesome looking and got me to check your gallery, ran into  'kitty blinking' <--love that one. 'rotating bunny is great.

anyhoo, all the questions you ask seem to point to things I've commented on so I'd thoght I reply with some answers but mainly to say I like your work and hope to see them get even better, in that nerd pixel way.