I figured I'd look into it later, so I talked to the new boatmaster. I noticed there was a new dude there who can boat me around, all cool - but at the end of the dock where my arrival ship once was, the barrels and chest that were sitting on the front end of the ship were still there, floating in the air above the water. Until I went back to the dock I arrived in. First thing I did was run around town, Rebirth was working without issue, no meshes or weird stuff. So got through checking in at Seyda Neen and was good to go. Added the path to openmw.cfg, as well as the BSAs as intended, so I didn't have anything weird happen when I ran it. Everything was fine, no errors or anything weird. This lets me make a new character and load a fresh new map every single time I add a mod to make sure it's clean, and that I don't have a save issue or whatever.

I exited without saving as I always do until I get the game how I want it, where I then start my playthrough character. Ran around Seyda Neen, to Balmora on foot, and enjoyed the new city stuff and all of it. No mesh errors, no load errors, nothing - all gravy baby. Installed Morrowind Rebirth into OpenMW, made sure the file structure was correct, added path to the openmw.cfg in MyGames/OpenMW as I was supposed to, and ran it, everything was perfect. Ok, so I installed OpenMW into a clean Morrowind, ran it, everything was perfect. Title may or may not be misleading, depending on whether it's a compatibility thing or not.

How to install morrowind rebirth