I'm not sure on using other maps directly for OSM, I'd personally try to stay away from it and instead use raw data.

As for the gisdata link, it looks like Fulton County significantly revamped their GIS data portal. I see some data sources which have no license (so you'd need to contact the owner/publisher for usage information), and some others like https://gisdata.fultoncountyga.gov/datasets/structure-footprints (which has a custom license, can't tell if it means it's fine for using in OSM) and https://gisdata.fultoncountyga.gov/datasets/JohnsCreekGA::address-points (which is CC-BY, so I think it's fine for OSM, but you'll want to reverify that). In short, you'll want to be careful about each data source's licensing.

This address data came from Fultn County. See osm.wiki/Address_Data_Import_for_Fulton_County,_Georgia for the import details. Note that the import hasn't actually been fully done, mostly due to the lack of time on my side.

During the import, I tried to correct some of the addresses and building shapes to match satellite imagery; some buildings were just rectangles, and address nodes were either far from the actual building or between buildings, so I had to make a guess on what was correct.