Preparing models for Turbosquid and etc.

Hello guys, I have some questions about the work with stock services for 3D.

  1. Which exported files make sense besides .obj and .fbx for animation?

  2. How to manage subdivision modifier? Do I have to make two obj files with subdiv.mod. applied and just a clean lowpoly one, without modifier in stuck?

  3. If there are customers here, could you please share, what common mistakes you observe, or the things that could be done better?

  4. What is better, to post models everywhere, or to be an exclusive seller?

Thank you