Image sizes

Hi, just started our shop and I have designed several different items using our own brands. However, what I have read, you can’t save items bitl logos on different locations like front and back right?

Second question: We have created logos that we want the user to be able to add to sleeves by designing them selves. But what’s the maximum resolution for this pictures, can’t find any recommendations regarding sizes of different locations.

Thx in advance / Alxz / CITYUPTAKE