Upload & Sell: Off
+1 for a single catalog. Only a single catalog gives you access to the full search and selection and collection facilities across all of your images at one time.
Just make lots of backups of the catalog as you go, and by that I mean lots of separate backups on separate drives, both on-line and off-line. It is important that you give yourself time to recover from old backups before any problem with the catalog passes through the entire backup set.
Catalog problems are not restricted to random faults. They can include cases where you alter or delete more images than you expected to due to more images being selected than you realised. Such cases will not cause a crash or error message and may take a while to become evident.
I backup every time I exit Lr. Those backups go into my general backup system but I trim the original backup set after a month or so to avoid filling the primary drive (a relatively small laptop drive). On an Apple system Time Machine helps to maintain a long-term chronology of backups to one or two drives.