Hi
I think your on a good track with the RBAC approach. I have a simular situation, where we build the cms for our customer but the customer has also some accounts to manage content themselves. Creating a custom condition, which ensure the user accessing a specific content-type in the content-manager have the permission to see and edit it.
The developers of Strapi already made a similar condition by default:
You can create your own conditions in /src/index.js and register it as descript in the first link above.
P.s. Working on my condition i found a bug trying to filter the user listing by email. see this issue on github
Hope this helps.
Regards
raphaeldas