How would a marriage-based I-485 affect my pending EB-5 I-485?

You can have two pending green card petitions running in parallel at the same time. Both petitions will be adjudicated on their own merits. USCIS will require you to use only one petition as the basis for adjustment of status when either the I-130 or I-526 petitions are approved.

I would not file a second I-485. This is an involved situation. You need advice from an immigration attorney who has evaluated the situation in more depth. A consultation appointment is the appropriate forum for you to get legal advice that you can rely on.

File the I-485 on the I-130, however, you have to withdraw the I-485 on the EB-5.

The USCIS has an established procedure for changing the underlying basis of your adjustment application. This needs to be done before the adjustment application is approved.

Two I-485s may pend at the same time. At the time of adjudication, you will need to withdraw one of them.

You can simply file the I-130 and request USCIS to connect it with your pending I-485 for the EB-5. Might save you some time. When CIS approves either one of them, you will become a conditional, lawful permanent resident.