I have around 1,500 TV Shows and 10,000 Movies. I’d like to know how much disk space will metadata be occupying if I add everything onto infuse.
That’s a pretty good sized library. 
I imagine Infuse might cache 1-2GB of artwork and other data for these videos. After adding your videos, you can view the exact size of cached metadata in Infuse > Settings > General.
Till 5GB its reasonable to keep the metadata, cause up until now I used to add only the shows I watched to the favorites for the metadata.