From a content development perspective the use of git is not ideal as compared to using SVN as SVN requires a lot less work to set up for a group of individuals who are not very efficient in setting up the network requirements.
Another consideration is art content does not require the same level of source control as code does so locking files tends to have a negative result as to the need for on going iterations and since art is a visual component it’s easier to monitor environment development via project management than software control.
The real problem getting X number of developers working on the same environment is the lack of a proper CMS system and the requirement that all build assets have to be visible to the project so the only way we found that works is to break the project into blocks and the project manager would assign those blocks as a task.
The set up would start by gray boxing the layout using simple primitives that would define the volume of space to be filled. Once the layout is done each block is saved as a streaming level and set to always loaded with the source volume saved with in the project folder. The ideal is all elements needed as part of the environment is contained with in it’s own level with the persistent used to only included the levels required as part of the environment.
The result each time the persistent level is updated all the blocks that have been updated by this process is loaded in with out the fear of stomping on someone else work.
To see how it all should work in theory check out any tutorial on the x-referencing feature available for 3ds Max. Referencing has been used for years on much larger projects.