The size in xB of your images does not really matter. More important is the quantity of images.
Some report that they have more than 100k images in one catalog. Personally, I prefer one single catalog - to me, the library function simply makes more sense this way.
The number of the images is more important than the disk space they take up. Even then, the number is not all that important.
The concept behind using multiple catalogs is one of grouping the images such that you would never want to search over the multiple catalogs at the same time.
I use multiple catalogs: one for my personal photography, and multiple catalogs per year for my event photography.
The multiple catalogs for the event photography work well for data archiving both the catalogs and the images.
The LR catalog is a SQLite database. I would consider splitting my personal catalog only if the database file starts getting too big for the OS to gracefully handle, whatever size that might be without looking it up.
That said, there is currently a known LR6 problem with the ZIP backups of the LR6 catalogs when the uncompressed catalog is more than 4 GB (?) in size in that many unzip utilities don't properly handle files that big.
Especially for beginners, one catalog is the way to go. There are really very few drawbacks, and significant advantages.