Why would they schedule a Disposition hearing in an adult criminal case after an Arraignment hearing?

Nothing to worry about. The prosecutors submit these motions to change counsel numerous times throughout a case. Normal course of business for them...

I need to see the documents in order to give informed advice.

Normally that is just moving which prosecutor is assigned to handle your case and is very common

This is normal in St. Charles. Depending on which circuit court division the case gets assigned to, it then gets assigned to a specific prosecutor that usually works in that division. If you have specific questions about the case, speak to the defense attorney.