Hello, for the zine art the requirements are as follows :
Horizontal or vertical, it is up to you and whatever you prefer for your illustration/concept art.
At least 2000x2000px and maximum of 6000x6000px.
The page ratio is up to you but the canvas height/width should not go above or below of the suggested sizes (i.e you can do a 4000x3000px canvas)

The merch dimensions are different depending on what you'll do - and all dimensions and specifics are listed in our discord server that opens once we have sent out all the emails :)