But a tag is all it is. Until there is a release announced on the blog and/or on the download page there aren’t any official releases. The only thing the RCn tags indicate are next steps towards the v5 release.
In regards to your questions, I personally switched over fully to the nightlies with RC2 and will handle upgrading individual projects as I get around to updating them. But, I’m just a hobbyist and don’t use KiCad for business. (I don’t even design circuits and boards for a living, I’m in hardware quality and break my employer’s products to ensure we design quality products.)
I want to run an intro to KiCad class for my local maker group, but I’m waiting for the official release before that. Hopefully the release will be soon so I can get a class (or series of classes) put together for the fall.