@Gisk I imagine people will be posting shorter, more brief posts in this roleplay. Collabs are okay, though personally I'm not too much of a fan of writing them myself. As for post guidelines, I'm not looking for anything in the context of a GRRM novel describing your character eating an apple just to fluff out to some arbitrary word/paragraph count or minimum. I do ask that posts aren't just rushed out, though, to give others a chance to respond so an entire page isn't solely just two characters conversing back and forth.
Regarding your collab question, I think I'll try implementing post deadlines to motivate people to reply. Given that this roleplay will more than likely have short posts, how does once or twice a week sound? That said, I do think this would be a more case-by-case issue if it does ever come up, with different solutions to it. Maybe it'll be asking the player for advice/temporary NPCing, maybe it'll be a GM event to break up some of the stuck interaction, or even just waiting a day or two for them to get the post out. In other words, how any other SoL RP runs.