Yes, putting fiberglass reinforced panels on the walls in the basement kitchen would be a good start.
We've actually done a reasonable job closing holes along the outside wall on Shattuck and 48th. But there's probably gaps in the siding on the South and West side of the building as well. Plus access via the cypresses and roof.
Internal walls are still major thoroughfares for rats though. I know there are/were rodents in the wall between the trash room and CCL, because we blocked several mouse holes in there. There seems to be access from below the cabinets in the upstairs kitchen to the area above the entrance corridor to CCL.
And of course, the entire crawlspace under the building is a giant rat playground, and connects to the basement kitchen and other areas, as well as directly to the ballroom.