Are my UVs okay for Unreal Engine?

I’m trying to model a gun for using in Unreal Engine.

Here is the model:

Here is the combined UVs:

Here is the UV of a single part:

My question is that are my UVs okay? How can I optimize it for use in Unreal Engine games? And in the combined view why do my UVs appear almost like a solid object?

You probably shouldn’t have the combined UVs to use in Unreal because it’s going to generate UV errors…overlapping by a ton, outside the 0-1 UV space (pieces extend a bit past the outer border), and they probably also have skewed UV islands. The UV for the one part looks alright, so in importing to UE set the property to maintain the UVs, or at least disable “Generate UVs” for each imported part having a UV map. I’d suggest trying to generate lightmap UVs in UE via the mesh editor. If it doesn’t work, try lightmap UVs in Blender and import those, again disabling “Generate UVs” wherever there’s a property for it.

Usually moving items don’t need lightmap uvs or any special attention.
Depends on usage.

Performance wise, 1 material over the whole weapon is far better than several material areas.