As far as I know, what you are asking for needs to be done in your 3D modeling software. You create your entire “car” or whatever with the hundreds of individual parts and then you can import the whole thing into UE4 and create one blueprint out of it directly. As long as your car uses separate meshes in the 3D software they will be individual meshes at import. If you group them they will be imported as one mesh. If you have 100 individual meshes already you can import them all into UE4 and then you would have to individually add them to a blueprint (I tried selecting multiple meshes and adding to a blueprint didn’t work, must be one at a time). Once they are all inside a blueprint you can drag them all out as one “actor”. As for the HISM thing, again, you can’t do that with different meshes. Each mesh would be its own “HISM”. I am not sure that would save you any performance.