Reusing same meshes throughout the game

My friends and I are making our first big game and we were wondering about some good practices about assets production and usage in the project. I had this doubt about whether we should model each level in Maya and export it as a single .fbx with submeshes or if we should export each submesh as a separate object. We decided to export it as a single .fbx, with the submeshes following some guidelines about the ordering in maya, but then I thought about the assets which will be reused along the same level, for example benches, rocks, etc. Is it ok if they are placed in maya and then exported altogether as a single object, or should we export them as separate and compose them in the editor? Will there be troubles for memory management and optimization if our levels are exported as chunks of like an .fbx object per room?

Thanks in advance for reading, if you have some reading to advise or any thought on the matter please let me know.

F