How can I file a marriage-based I-485 petition with a pending I-829 petition?

You do not have to withdraw your I-829 before proceeding with your I-485 application. Both applications can be simultaneously pursued. However, in the event that one of the applications is approved, the second application will be withdrawn, usually by the USCIS, since you are only entitled to one green card.

Since your I-829 petition is pending, you are a conditional permanent resident. A conditional permanent resident cannot file an I-485 application.

The best way to do this is to file the I-130 marriage petition and designate consular processing and then surrender your conditional EB-5 green card and apply for a new conditional green card abroad at a U.S. consulate. It is not so easy to process this in the U.S.

I just handled something similar and suggest you go ahead and file the I-130/I-485 without withdrawing the I-829. At the interview, you can bring a letter to withdraw the I-829 and I-407 to abandon your green card if the marriage-based interview goes well.

No, you can have both filed if you qualify for both. It is not an issue.

More than that, you have to give up your green card. Then you can file to adjust status.

A permanent resident cannot adjust status. You should indeed withdraw the application and/or seek consular processing for the I-130.