Knowing in advance that all of your preferences are not nearly as close to canon characters, I ask you not to be skeptical before you give this a go. We all know that Supernatural is a very fine and expansive world, which means it can reach out and welcome both canon and non-canon characters. I won't lie about my intentions here, I really want to try and make some SPN connections if that's possible, but it would certainly be awesome to have some OCs come in and join the fun. I'm writing here as Sam Winchester, and I'll bring my Lucifer if the opportunity arises. I'm very open to any crossovers that might want to join in. So don't be shy.
The story itself is that there won't be any story guides here. Anyone can just come in and start an interaction with Sam. Say you are an OC and you have some leads on a case that Sam might be able to help you with. You could just do that. Just use your imagination. Sam would be more than happy if someone could find his lost shoe. Pun intended, haha.
All in all, whether you are a Dean, a John, or just someone playing your own OC, come on in and write it up. This is all very new to me, and I'm still scratching the surface and digging my way in.
I'll write 1-3 paragraphs for this group, if not more. I'm friendly and very open minded.