What is really interesting is the way how you are going to keep data safe. Do you have specialists with a good experience at such tasks? And what about storages? I can imagine amount of private data you will need to store and keep secure.
1) When designing the system, a separate security specialist was involved
2) We order audit of vulnerabilities from third-party specialists
3) We have a bounty program to identify vulnerabilities
4) We use a proven data center for secure data storage