Alright everbody I have an update!
For starters, it turns out that both display ports are working, and dual monitors do work. However, I was using a display port to DVI adapter and that was what didn't work. If both connectors (HDMI and DP) are using naked connections, they work fine for a dual monitor setup. I tested this with a DP monitor and an HDMI one.
Second, I'd recommend using Opencore on this machine now for Catalina, it's much more stable. I am running the latest version of Catalina (10.15.4) using Opencore.
The SMBIOS is best set for an iMac 2019 - I'm using it currently (and have been for the past month.) No issues whatsoever on my end, everything is currently working.
I have native NVRAM working, (no emulation) and my sleep works fine, even when powernap is turned on. All my USB 3 ports are showing up correctly. I have native wifi and bluetooth with the BCM94360CS2 and an mgff adapter.