Yeah I have a tendency to add details ( sometimes too much, like this one). Also I usually have trouble making 2 pieces with the same colour to be distinct from each other, in this case the body and right arm looks like they are blended. Do you have any idea how to fix this ( reshape / different colour choice / etc )?
You don't need to pre-zoom your art for PJ, the site has a zoom feature. If your whole piece fits as the preview image, you don't even need a detail file at all.
The character is difficult to read. You put so much detail (dithering? lines? I can't even tell because there's so much) into everything that there's no room left for shadows to show the form or distinctions between different major parts of the armour. "Less is more" is a cliché for a reason :]
Shadows are a common way to handle it distinctions between parts. The light doesn't hit every part of the body equally.
More generally, you can also be more clever in your design to highlight/distinguish important parts, such as by making the arms be covered in a different material from the torso, or putting some distinct pattern on them. This is a common issue in character design in general, especially for stage, film/TV and 3D video games, where you can't always rely on lighting to make characters read well.
A trick you can use to suggest a lot of detail without cluttering up your art is to only show detail on the edges between light and shadow (or, more broadly, at the edges between different colours). So, instead of a straight edge, you'd break it up to show the surface details, but don't show those details elsewhere. It works really well for medium-size sprites like this, since you have the room for these "details", but don't end up left with huge flat areas of colour. It can work for larger art too, though it tends to give a more stylised appearance then.