Hiring anyone at all is a significant hurdle in much of the EU, whether it's from your home nation or another member state. If we're talking about startups just starting to grow beyond the founders here, you're not going to have anyone on board yet who is dedicated to dealing with HR, legal and payroll issues. Those won't necessarily be a full-time job with employee #1 either, but they're already a significant overhead the moment you start looking to hire that person, and if anything unusual or adversarial happens it can quickly become an actual full-time job.