Kareem,
As for the Portal scaling:
Configure Portal Database Clustering - CA API Developer Portal - 3.5 - CA Technologies Documentation
The MySQL Cluster would need to be on a separate system from the API Portal, and it would need to be deployed and managed by your team. We do not have MySQL Cluster installed on the API Portal, and we don't support installing the MySQL Cluster components on the API Portal itself.
You would need to have a MySQL Cluster deployed and configured before you can follow the steps provided in the Portal Installation document referenced above.
So to answer your question overall: We support the API Portal connecting to a MySQL Cluster to improve database performance and redundancy, as long as it's off-box.
-Alec Daniello