haha...now for my 2 pesos worth...
somehow, i think if you're rather young (under 13) and you want to have a natural look for your cosplay, don't use too much eyemakeup or lipstick. dark eyemakeup can make you look too old, so keep the colours light, and the mascara minimal. for lipstick, just stain your lips by dabbing the colour on, then apply a top coat of gloss.
enjoy your youth! don't try to grow up too fast!
clinique has a good range of products for sensitive skin, especially the foundations and loose powders.
p.s.: kai! good thread!