As for the paint, you'll probably want 2 things-- one for your face, and another for the rest of your body.
For your face, you'll want a theater-quality paint that will stay on. Mehron's paradise line (which is what I have on in my icon) works really well even in heat/humidity. Ben Nye is also a solid choice.
PAX is the way to go when it comes to painting the rest of your body, though. Note that body painting like this will mean it'll take you a few hours (yes, hours!) to get your whole cosplay on.
Personally, I'd invest in a bodysuit of sorts so that you could just paint your face/hands. A bodysuit would also give you something to attach Stitch's extra arms/spikes to, if you were going for that.
Good luck, and can't wait to see it!
DeviantART // Tumblr // Facebook // Instagram // YouTube
- Space Rebel Matt Holt (Voltron): ??% (Sewing) Anime Boston 2018
- Gym Uniform Todoroki (BNHA): ??% (Planning) Spring 2018
- Dancing Star Night Akira Kurusu (P5: DSN): 95% (Final Details) Anime Boston 2018
- Lapis Lazuli (Houseki no Kuni) : ??% (Planning) Konkon Spring Shoot 2018