Ummmm... lol idk
Basically whenever I try to make a wallpaper, I try to get an image as large and clear as possible, but I don't have a particular size ratio or anything that I go by.
All my (current) wallpapers are created on 4020x2261 canvases (about double the size of 1920x1080), but most of the base images are a lot smaller. If I had to give a number, I'd say most of my base images are about 1000 pixels tall, with the smallest I've done being probably 700 or so.
If you'd like to request a certain image, just send me a message in DMs with what you'd like me to do! More than likely, whatever you have should work.