Keycloak Fitment For My Application

Currently, I have a spring boot application where we have multiple organization and these organization have multiple users. These users are authenticated via JWT as of now.

Wanted to understand the fitment of keycloak, with scalability ( considering creating realm for every organization).
Also, we will maintain users on the application too,
so does keycloak provide a way to link so there is no inconsistency between keycloak and the application?

It will be really helpful if someone can provide quick insight on this.