Lightroom Classic and Lightroom CC can inter-operate, but with some restrictions.

Classic is a more sophisticated editor; many of its features are not yet in CC, even though they share the same ACR engine under the covers, for example selective item presets, red eye correction. A good feature comparison is here (scroll down past the decision flowchart). So edits done in Classic are not fully compatible with further editing in CC.

The bigger issue is sync. If you have them tied together, images you import in CC always go to the cloud, and will sync down to Classic as original images. On the other hand, images you import in Classic have to be specifically selected to go to the cloud, and when they do only a smart preview goes to the cloud, not the original. You cannot ingest in Classic and have originals go to the cloud. Quirks in subsequent activity (like edit-in-photoshop) can make it confusing what you have where. Further, keywords and color codes do not sync properly between (especially up from Classic).

Fundamentally it appears Adobe did not intend Classic and CC to inter-operate smoothly and completely; it is more like "Lightroom Mobile" sync from LR6 on steroids. CC however inter-operates very smoothly and transparently with other versions of itself on many platforms, which is its real strength.

You can use them separately, provided you are not syncing with the old LR Mobile feature -- that is the same sync and same cloud account that CC will use, so you can keep Classic purely non-cloud and CC purely cloud, but you cannot mix and match. If Classic is set up to sync at all and CC is using the same Adobe account, CC will sync back to Classic.

It is worth noting there is no explicit catalog in CC, in the sense of it being a thing you can create more of; it is just the cloud. Sync's from CC to Classic go into "mobile" collections in Classic's catalog. Only one catalog on one computer can sync with CC at all (a key limitation is that CC cannot be used then to keep two Classic catalogs on different computers in sync with each other, something long requested).

I am sorry I do not know what VV is so cannot address that.