I have about 700GB total of mostly free add ons from flightsim.to and purchased add ons.
But I have all my add ons organized into folders by country and I use msfs add ons linker to only link in the ones needed for the regions where I plan to fly. I could never have them all loaded at once but I do load over 300GB at a time when I load all my US/Canada add ons.
It does seem to take a longer time for the initial load of the app and maybe a little longer on flight loading too when I have a large amount of add ons loaded. But performance during the flight does not seem to be impacted, only the initial startup and load times take longer.
I highly recommend using add ons linker so you don’t have to actually move files around or rename folders.