PJ has a forum with a WIP section for just these kind of questions.

Personally, I would keep it shaded in a cell shaded form so you can see the volume of the creature. How many frames is dependent on game specs and whatever restrictions you've set for yourself. If you have none then, my suggestion is to work on a 3 frame ani and then add frames as needed until it moves and behaves as you envision (or close). This is helpful in developing other sprites too. If this is a boss (a complex sprite) and it ends up, say 8 frames, then lesser enemies can be 4-6 frames, see?

Once the animation itself is made, the frames, you can at that point come back to the frames and dither away to match your concept art. You can even go way advanced and sub-pixel.

Yes, pixelart is all manual and with animation is frame by frame, pixel by pixel...don't disappoint us ;)

Use the forum's WIP section (link in menu) for the most enjoyable flaming of noobs help from others who are more adept at animation than me.

There is a feature on 'stickman' on the main gallery page that deals with animation in pixelart that you might learn a thing or two from. Looking in the forum resource section is treasure filled too.

nuff' go!

 Thanks for the response. Yes, I'm VERY new. Not new to art or animation, but pixel art is fairly fresh territory for me. 
I think I did the dithering just to see if I could. I could get rid of the dithering (and the shading entirely).

I actually don't know where to start with the next frame. In an idle position, I was thinking it would just have two or three frames of bobbing. The movement would also be pretty simplified to two or three frames. But all-in-all that could involve almost 10 new drawings. I'm certainly new and I'm ready to learn... is there an easier way to do it? Or is it really frame-by-frame?

Very nice sprite.

Just know that in game sprites with animations, the use of dithering can be extra challenging and is considered an advanced skill. Not knowing how 'new' you are, you may consider using solid/cell-shaded coloring instead for your platformer. This shouldn't deter you if you feel confident, its just info best learned now, k. Welcome to Pixeljoint.

loving it, its looks fantastic well done =] rated 5 faved =]