The engine wont be drawing anything you’re not going to see. So no back faces.
40k is WAY to high for a lamp by the way. If you want to make a game out of it, that is.
8-20 tris is absolutely fine, you could to may 1k tris at LOD 0.
But if you got 40k in the level, you’ll need to use instancing. That way, it’s only 1 draw call for the whole lot, because they’re basically the same thing.