So, my question is, If I reinstall future updates of KLAS (or any further packages -KFLL, KDFW, etc.) will I have to re-install AddOn Manager X AFTER the installation of any of these airport packages to ensure the KORD doesn't lose its scenery?
No scenery will lose its buildings when you install KLAS, because KLAS installer updates all the sceneries you already have to a version compatible with it. The only way you might lose the buildings, is if you DID NOT had KORD installed when you installed KLAS, and then you install it using an old installer (not the one that is currently online)
In this case, as explained many times already, you can to any of the following 3 things, and ALL will fix the issue:
1) reinstall KLAS, so it will update KORD
2) download the current stand-alone Addon Manager, so it will update KORD
3) re-download the current KORD installer.
There's no difference at all, all 3 will fix KORD (and Zurich as well)
So, to reply to your question, since you already re-downloaded KORD, you already have a version that is compatible with KLAS so, it will just work, without doing anything, and regardless of the order you install it.
If you don't see buildings at any stage, DON'T DO ANYTHING. Try to simply see, on that moment, if you have both the Addon Manager and the Couatl menus. If you don't, don't do anything, exit from FSX and restart it, and see if gets sorted it out by itself.