Outsourcing level designing to freelancers.

What are the best practices to outsource level design.

I see particular problems.
- I have relatively big project (about 30 GB)
- I'm using third party like Gaia/Vegetation Studio, I guess my freelancers will have to own them too.
- I will have to share my source with some unknown people (I know I know )


Frankly speaking for objects placement I could even reconsider pulling out my own exporter. Something like grabbing all positions orientations and scales of prefabs on scene and recognize them by name, all this saved into a text file so it would be imported into my project.

But there is still a problem with materials, terrain and third party.



Alternatively would it be possible to create two projects sharing scenes and some assets without sharing everything in project.