wow, its fantastic and for your first attempt, it is a very good start.
In my opinion there is not much that I can see here that needs improving asides from a few stronger highlights in certain places, and I thought over all your image was a bit dark, so I brightened it with a smidgen of color balance.
I am not experienced with dithering myself so this seems like a fine attempt at that discipline also.
The highlights I added were randomly chosen levels of shades so if you where on a restricted pallet I have probably exceeded that now. I am not used to restricted pallets.
Anyway I think you have enough colors in your original image to do something similar to what I did with the highlights, I just got a bit lazy trying to find the ideal shades that already existed.
Oh I thought if you are up for a challenge, and to have a nice compositional feature, .. put a shot glass beside the bottle, (half full) and make it sit so its covering a bit of the bottle.
keep it up