Redfin type map clusters and reverse geocode

I’m in the process of migrating from Google maps. I need help with creating clusters based on the LatLngBounds. The logic I’m struggling with is:

  1. How to obtain all US zipcodes/counties/states within bounds?

  2. Display cluster in map

1 - the only thing that comes to my mind is quering Search API with bounding box defined and idxSet=Geo set. But that is not a typical case, so it might not be an optimal way.
2 - There is an example that is showing how to show clustered markers -,map,markers-clustering.html