Hello MTH
You can try using the DataGroup Explorer for this purpose. In the DataGroup Explorer, from the left tree, if you select the Schedule for the element (e.g., wall or door etc.) you want to create selection set for, and then in the schedule in the right side, if you sort the list based on the property you are looking for (e.g., Type), and then select all the elements for that type(e.g., "Interior" or "Exterior") using the Shift key, then all the required elements will be selected on the model as well. Then you can separate the levels as per your requirement.
Satadal