Hello again,
I have not tried the other alternatives to Enscape. For the size models I do Enscape has been fantastic. I deal with single family homes with file sizes that range between 30 and 100 MB. Your mega project is a at least one or two orders of magnitude larger and thus needs serious considerations of how best to work with and what best methods to output for users.
I’m just an architect, but it seems to me you need something that supports massive environments that can load portions within a certain range of what is visible to the user to best utilize the computer resources available the way video games such as Grand Theft Auto do.
Unreal Engine comes to mind or maybe Unity. I’ve never personally used these, but hopefully this leads you in the right direction for your needs. Maybe reach out to forums on Reddit that focus on Game Creation to see what the State of the Art is and find out what people are using the most.
If you stay with SketchUp and give Enscape a try, focus on optimizing your 3d environment in every way possible.
- Reduce entity poly counts to the bare minimum needed. Objects that are only viewed from far away such as the top of a tall building can probably be very low poly towards the top, and higher where users might get close. There are Plugins that may help you with this, or you can export to MeshLab and try optimizing models there.
- Use the Material Resizer Plugin to control the image data within your materials. Again consider if users will be able to get close to the surface or not and reduce the images to the bare minimum needed.
- Use components for duplicate objects.
- Use proxy models. Enscape has a library of its own models you can use. In SketchUp you will see a simplified proxy model, but when you render in Enscape, a highly detailed model will appear. Note you probably cannot export the Enscape models to use in other software.
Good Luck! 