Advice on account console and property customization

Good evening,
for an upcoming project we are looking into using keycloak. It would solve most of our usecases, however we would have to extend the registration by a custom field and implemented a bit more elaborate email validation.
For some operations (group assignments) we are currently considering the keycloak API.
Furthermore, we would have to customise the design. Maybe some of the features of the new account console will come in handy.

Especially the first two issues seem to become a lot simpler with the User Profile SPI.

Is it worth implementing these things with the (then) legacy providers?
Has someone here already attempted to port existing ui customisation (esp. colour schemes) to the new account console?

See:

If I understand correctly these are related to the login form, but not to the (new) account console?

However, thanks for these guides, they did help a lot when I was customizing the login page for another project.

Does the (new) account console have an associated FreeMarker template?

The new account console is also very flexible, using react one can add pages and there are css variables one can override to change the look and feel. Have a look at this PR for an example:

That looks promising.
Thank you for the hint.