Hello, what size should be apply for product picture?

Depends on your products, i.e. how much zooming you want on the product page for example. The primary image is shown in 320x320 by default I think. I would go above that, so let’s say 640x640 for higher resolution devices. But it’s really up to you. It’s not like something breaks if the image is 2000px – but it will load slower.