So if you’re trying to make a BP of your mesh there’s a number of ways to start going about it.
You’re going to want to derive from the actor class, so just click actor up here and rename it to whatever you want then open it by double clicking:
You’ll then be greeted by this screen:
That object in the center is the root object, you can replace that in the top level with your root mesh. Just know the root will no longer have a translate gizmo because it is the defacto center of your actor.
Now the BP viewport functions mostly like the unity prefab window with a few differences that shouldn’t effect your use case. Here you can either drag in your meshes from the content drawer or manually add them and nest them by hand in the components window in the top left. This window does take into account the pivot of your models so if your pivots are all zeroed out and your pieces in their correct place, they may drag in just fine. If their pivots are based on relative location to their parent piece, you can parent them (by dragging and dropping in the component window) then going back to their details and zeroing them out.
Now remember blueprints aren’t just containers, but also actual classes themselves so you can handle any logic you need on them as well if you want to. Do you need any logic for these or are you just doing a visualization?