Hi Lei Y., my team loves your Sticker Set style. ^_^
We are on a fast deadline, so simple is okay!!
.AI vector drawings with transparency, would work better for us, so our team can animate them.
The .PSD chibis are also cute, but would require extra 2-5 layers, such as showing a wink, hearts floating, or tears crying. :)
Deliverable would be .AI or .PSD file with layers.
We could try 2-3 "stickers" in the first hour, to see how we work together. Please message us for the first assignment today, if you are interested! ^_^