I'd go Django, even if it's just to prototype the system. If you need to microservice out a django install, just grab all the views and turn each into it's own flask instance with the rest being a collective lib. Coming from a sysadmin perspective, python apps require slightly less resources than a java apps do. Plus, like someone else said in the thread, it'll be easier to onboard developers at any knowledge level so it's great for beginners and advanced users.