I know a little bit about Maya from watching other people’s youtube videos but have not used it myself. Basically, I think you get a static mesh (or skeletal mesh) per object in Maya. So within an object you can have as many mesh pieces as you want - UV Shells I think they are called in Maya - it will still be imported as one mesh.
Your choice of origin depends on whether you are expecting to have multiple instances of the mesh. If you are kit-bashing and therefore expecting to have multiple instances, then you would put your origin somewhere useful for the piece rather than using the origin of the entire scene. So for example, for a door that you expect to use multiple times, the origin would be most useful to be on the ground on the side of the door where the hinge would go (so you can rotate on the Z axis using that side easily) and would not be set relative to the scene origin. And this principle would apply to wall pieces, streetlights, road pieces, wall pieces, all kinds of things you know you will have more than one of.
But if you have hero pieces that are only used once in a scene, like a fountain or a big building you are never going to be able to go inside, you would probably set the origin relative to the scene. And anything bigger than a house you would probably split into pieces anyway, for technical reasons.