Great question! It seems like there is at least one other post that asks a similar question. In general, you should upload all of your data to Cesium ion, yielding a single URL that will load all of your data. The data you provided is in a format accepted by Cesium ion so this is certainly feasible. Sadly, I do not know of an elegant way to “merge” 1000 large 3D tilesets if you are hosting them yourself. I will check in with the Cesium team and let you know if anything comes up.
-Sam