Hi there,
It’s really personal preference.
I would say that you can leave the existing content as it is, but start using Gutenberg editor for new content.
Should I be using Gutenberg instead as its features will allow me to ditch many standalone plugins?
I can’t really answer that unfortunately as I don’t know what features/options you are looking for.
I would start by testing the available Gutenberg blocks first and see you can achieve the desired layout. If so then you can definitely ditch the other plugins.
Let me know if this helps 🙂