How do I best apply for my EB-5 AOS and why are they being transferred to the California Service Center?

You do not need the fee bill to file the adjustment. It is up to USCIS where they are routed. Instructions are to file with a lock box and then they re-route the file.

The only reason to pay the fee bill would be to freeze the age of your child but since a Final Action Date AOS filing also does that, you should be OK. All the EB-5 based AOS cases are being processed at the CSC.

If you are applying for adjustment of status, you should not pay the NVC IV fee bill. That is required only for immigrant visa processing at a U.S. Embassy or Consular Office abroad. As for the transfers, the USCIS moves AOS applications around based on its resources and internal adjudication policies. You should follow the filing instructions on USCIS.gov regarding where to file your Form I-485 application. If the USCIS transfers your case to another office, it will send you a transfer notice. Your case number for tracking purposes will remain the same.

The California Service Center processes all EB-5 adjustment of status applications. If there will be an interview, they may forward them to a local field office. You do not need to wait for the NVC fee bill. You can file as soon as your application is ready to be filed.