Make it as modular as possible.
Plan out areas which can be split off and abstracted.
Make use of the proxy function in xrefs.
Use render/multi instances as much as possible.
Once assets have been approved, bake them down and simplify them as much as possible, particularly if they contain lots of generators e.g. sweeps/extrudes/booles.
If you can get away with using different levels of detail based on distance to camera, do it.
Absolutely better to use the subdivion surface generator, as that can be used in a rig to add levels of detail to the whole scene.
If you’re using a render engine that supports proxies e.g. Redshift or Vray, use them!
Finally, know that once you get past the 3/4000 object mark, your scene will slow to a crawl and you’ll spend 15 minutes waiting every time you attempt to load, save or close it.