Side by side would allow you to formulate queries depending on the use case, but of course this comes with quite some cost (keeping data in sync, having another system to take care of).
Neo4J allows you to store properties, so you certainly could model all your info (also the relational aspects) in it.
You might be able to simplify some of the queries using recursive SQL: https://en.wikipedia.org/wiki/Hierarchical_and_recursive_que...
Neo4J is a very popular DB (ranks #18 here https://db-engines.com/en/ranking) so should be mature.
Side by side would allow you to formulate queries depending on the use case, but of course this comes with quite some cost (keeping data in sync, having another system to take care of).
Neo4J allows you to store properties, so you certainly could model all your info (also the relational aspects) in it.
Hope this helps!