I did a similar project (file size wise) some time ago. I would probably go about it this way:
- Import the FBX into 3ds Max
- Split it up where it makes sense, doors, floors wall elements etc. Just make sure you don’t put to large chunks together cause that will create problems with the lightmaps
- Objects which look similar to each other, like doors, wall elements and stuff, reuse them as much as possible
- Poly heavy objects should be optimized or remodelled. CAD data can be a hazzle >< Alot of CAD data has polygons on top of each other (especially data from building models), this is something you should check ofc.
- Unwrap everything with two uv channels. For the second uv channel you can use flatten mapping in 3ds Max
- Set up proper normals
- Export the individual chunks in their own FBX file
- Rebuild the scene in UE4, and reuse as much as possible
That how I did it atleast :9