Ask HN: How secure should my site/server be?

I'm not new to security, and that's why I ask. I have created a "payment portal" integrated with Stripe for my [few] customers. I have gone through various guides for securing debian, apache/node, mysql on dedicated instance, etc., using https only, ssl certs, passed Qualys HTTPS/SSL scan with a 90%/A Rating, performed qualys and other vulnerability scans...but have I done enough? I'm not storing credit card info, but am storing username, passwords, and basic stats. I also developed the portal with security in mind taking CORS, SQL-Injection, and other tactics into account.

I know security is and should be considered at every layer, but when is there a reasonable amount of security when security is not my primary focus?