One FBX with whole map from 3D soft or create map in unity ?

Hello guys i want to ask some question about pros/cons. the thing is like this i have map let’s take De_Dust(probably everyone knows it :D) so what is better to have one model building in 3D software or to have separate models from 3D soft and build level in unity with prefabs ?

It really all depends on if you want to change certain models about or whether you just want to keep the original, static map. If you had separate models, you might be able to make the map dynamic, but this would be a little bit more heavier on both your CPU and your GPU. You will face copyright issues if you were ever to publish a map such as de_dust without permission. (Especially if you are going to be selling the game.)