Looking for Advice on Hiring Qualified UE Developers for Long‑Term Collaboration (Project Migration + Technical Ownership)

I’ve been developing a UE project since 2018 as the creator and designer. I currently have a fully functional prototype built in UE 5.0. I’m preparing to integrate a second minigame project, which requires upgrading the main project to UE 5.7.

I’ve hired multiple freelancers over the years — some great, some not the right fit — and I’ve learned a lot through the process. The biggest challenge has been finding developers who can take technical ownership rather than doing surface‑level task work. Recent attempts to upgrade the project resulted in major breakage, so I’m now being more careful about who I bring on next.

I’m looking for advice from people who’ve hired UE developers or built teams around long‑term Unreal projects:

1. What qualities or experience should I look for in a developer who can handle engine migrations and project stabilization?
2. How do you evaluate whether someone is truly senior‑level in Unreal (blueprints, C++, plugins, versioning, etc.)?
3. Are there red flags to watch out for when hiring freelancers for technical tasks like engine upgrades?
4. What’s the best way to pitch a long‑term project to attract developers who want stability and ownership rather than short‑term gigs?

I’ve always paid developers fairly and consistently, and I’m committed to finishing this project. I’m hoping to connect with people who’ve navigated similar challenges and can share what’s worked for them.

Thanks in advance for any insights - I’m looking forward to any advice, and seeing what your best practices are.