Hmm, in the EU, at least depending on the country, you treat an affiliate as an independent service provider and have zero paperwork. A bit like hiring a plumber or lawyer. Uber, Deliveroo, and co. tried that one on their drivers.

I think you really need to get professional advice. You will also probably want legal advice on the drafting of you affiliate program's T&Cs.

Edit: Affiliates are a very old practice and one does not need to be in 'SV' to grasp how it works for tax and accounting.