[Q] Can I submit both I-526 petition and I-485 to CSC if I am maintaining my NIV status in the U.S.?
No, there is no "concurrent filing" allowed for EB-5 cases, meaning you cannot and should not submit both I-526 petition and I-485 together at the same time. You have to wait until I-526 petition is approved, and if you are still maintaining your NIV status (note maintaining your NIV status is different from avoiding "unlawful stay" -- hard to explain it here), you can go ahead and file I-485 adjustment of status application.
Personally, I am not a fan of the concurrent filings because it raises too many issues. I am also not a fan of USCIS using lockbox addresses to receive applications.