Lightroom Catalog Conversion Sync

Got it.  Ok, then.  One catalog it is.  Thanks!

When you set a LrC catalogue as the catalogue which will sync (only one catalogue can ever sync), it will automatically sync down all files from Adobe's cloud. You've no control over this, so let it do it.

Once it is done, then check that you have everything you expected that you would have, so do common sense cross checks such as the number of files in the cloud versus the number in the LrC catalogue. Once this important step is complete, and you're sure that you've lost nothing and are in complete control, then you can make decisions about having more than one catalogue.

And as DJ Paige said, it's better to stay with one catalogue rather than fragment control of your pictures.

Also, I don't expect that converting from a cloud-based Lightroom ("Lightroom CC" doesn't exist) to separate Lightroom Classic catalogues would "increase processor/memory efficiency". It will mean less dependence on the cloud, and that you will be in control of managing your pictures, as well as having LrC's more extensive features.

I don't know the answer to your question 1 or 2, but I do know that the almost universal advice is to use one catalog in LrC. There are exceptions to this rule, if you have strong justification, such as when you have work and personal photos, those could go in separate catalogs, but catalogs by year is a poor idea.