1–if you haven’t sold the game/product then there’s no royalties owed
2–there’s no limits like that, the source is available for customization so you can expand it to support whatever you need
3–you can give it to someone else to distribute, it doesn’t matter if they continue to give it for free or not, if they sell it then they would pay royalties.
I don’t know what special treatment you would expect, if you are looking for some funding you can submit your project for Unreal Dev Grants: Epic MegaGrants | Apply For Funding to Enhance the UE Open Source Community - Unreal Engine