No, this is the right forum for this sort of question.  If you look at the main page you will see our descriptions for the levels. I'll paste them here as well. You'll see that casual is [i]generally[/i] one paragraph and Advanced is [i]generally[/i] two or more.  Not so strict as you would think. Keep in mind that GMs have the right to tweak the expectations of their own threads.  I tend to go between Casual and Advanced, dependent on what strikes my fancy in either level. I hope this helps. 
[i]
Free: For roleplaying involving one-liners, few-liners, speed-posting, and for anyone who doesn't want to have to worry about standards. See individual GM for RP specific standards

Casual: Roleplay here if you enjoy writing at least a paragraph or two, character development, and some depth. Grammar and spelling are encouraged. Generally one paragraph (a few sentences) per post. See individual GM for RP specific standards

Advanced: Advanced RP focuses on longer posts, often with in-depth plots, character development and extensive settings/lore. Must make a dedicated effort to minimize typographical errors and to use good grammar. Generally two paragraphs, but usually longer. See individual GM for RP specific standards[/i]