I would start by giving this a read:
Basically, what you are looking for is the Custom Mesh Component.
To load your mesh at runtime, I would guess you have to load from your file and fill in the FCustomMeshTriangle array from CustomMeshComponent (CustomMeshTris) as you get the data. Since that component herits from UMeshComponent, you also have control over the materials applied on it.
I’m not sure about the LODs, but you could get some tips from UStaticMeshComponent thats also inherits from UMeshComponent and supports LODs.
I hope this sets you on the right track!