[Q] What are possible USCIS responses or outcomes to the I-526 immigrant petition submission?
First, USCIS (specifically, California Service Center) can approve your I-526 immigrant petition, and send you an Approval Notice to prove the approval.
Second, CSC examiner of your I-526 petition can send you what is called RFE (Request For Additional Evidence) requesting additional documents or explanation on your case. Getting RFE may delay adjudication of your I-526 by around 2 months, but RFE is not something to get upset or worry about.
Third, CSC examiner can send you a denial letter. It would be a very rare case to deny your case outright unless the CSC examiner believes that your I-526 case cannot be approved based on a legal basis.
The most important thing about I-526 petition is to make sure certain documentary evidences can be obtained by EB-5 client to prove certain points. If this can be done, it should be no problem to get I-526 petition approved. Really, getting I-526 petition approved is not all that hard, although there may be a lot of paper work involved.