hahaha, I see that my good buddy Gabriel is working hard on the hottie at last
nice image dude! It already looks like a finished comic frame, meaning there is great stuff going on already!
To be honest, I’d play with the colors of Rita and the bus stop, and experiment for an hour or so, because now I see all the basic colors in the focal point of the pic, which could give you a hard time in creating a general mood. On the other hand, you could choose to keep those bright colors and really work on making them fit together, since it’s a bright sunny day it’d make sense, and that’s how I went with my own illustration actually. Or, you could ignore everything I’ve just said also. hehehehehe
About the image size: I think you’re working on a good scale, and it’d be totally cool with the challenge. On the other hand, I personally try to go as big as I can, depending on how exciting the subject is, because I always see my illustrations as being printed poster size in the future, by me at least heheheh. Only downside is the processing speed obviously. So my suggestion would be: you are already in the ball park for the challenge, paint the image as big as you would want to see it…
As far as the layers go: I used to paint exactly like you've described, which is not a very advatageous way i think. I guess the best way is: trying to reduce your layers to one layer per object, or something close to that, during the first half of your painting. During the second half of painting you'll be fine tuning, and adding effects anyway, which will increase your layer amount drastically. At least this was my experience...
hope these are helpful, cheers buddy
go go go!