When and how often should I follow up after my application?

Once and at the right time. If the recruiter promised a response by date X: follow up politely on that exact day. No date given: a short email after 2 weeks. Wording: 'I applied for [position] on [date] and wanted to briefly enquire whether my documents arrived completely and when I can expect a response.' After that: maximum one more follow-up after another 2 weeks. More than two follow-ups comes across as pushy — BA employment statistics show that recruiters often handle 100+ applications per position and responses are delayed. GDPR: you have the right to know what data is stored — also as an applicant.