If you introduce a bug bounty too early, you will be paying out for vulnerabilities that could be caught or prevented in a much more cost effective manner (vulnerability assessments, penetration tests, developer training, appropriate monitoring).
Sqreen also have a handy basic security checklist: http://cto-security-checklist.sqreen.io Specific to bug bounties they say "You need security aware people inside your development teams to evaluate any reports you receive."
Daniel Miessler has a good breakdown of when to consider various types of security testing: https://danielmiessler.com/blog/when-vulnerability-assessmen...
Sqreen also have a handy basic security checklist: http://cto-security-checklist.sqreen.io Specific to bug bounties they say "You need security aware people inside your development teams to evaluate any reports you receive."