Recently I tried saving a sprite sheet that was very long something like a width of 20,000 pixels and height of 256 pixels. Once I saved it as a png all it showed up as was a grey long box :/ Is there really a limit to how big a picture could be or does anyone know how to fix this issue ?

I believe the width/height are 32-bit integers so it should be OK in that respect. Perhaps it's a limitation of the application you're using to view the image?

Wouldn't it be better to make the image square and have the sprites in rows/columns, rather than one big long row anyway? It's gotta be tough looking at an image like manually...