I'm a little stuck on how much to shrink the reference image without making it tiny, but also without shaving off like 10 pixels at a time until it accepts it which will take quite a while, hah. Anyone know?

I have no idea, but the first cosplay I entered with, the reference image was 716x1279 if that helps you at all?

It does, thank you! ^_^ I'll just resize it to 700xY then, depending on what Y is when it keeps its proportions.

You're welcome :3 Glad I could help