I'm not v good with painting, but definitely try it out if you're interested !! if you're scared of messing up, just make copies of the layers you'll be working with so you can always go back to previous versions. your colours are always v pretty, so I'm excited to see the end result of this :D
You can do all the colors on one layer under the lineart before merging. Then merge when the more harder details are done haha makes it easier to keep the same um...shapes? The more comfortable with painting you get the less layers you need, also is good to do small things like eyebrows last or else you have to repaint over and over XD Good luck i'm sure it'll look super pretty :D