Which hook for reg form after validation

Hi, which hook do I use? This is for a custom registration form. The hook needs to be:
1. AFTER ‘submit-form’ validation has run, including any custom validation
2. AFTER user has corrected any validation issues
3. AFTER final validation has been proven
4. BEFORE writing the validated new user field info to the DB
5. BEFORE anything other actions, including (such as post-registration redirects, showing success message, etc)

Thanks!