During installation you at least need 20Gb on the main disk. Once installed you can move some things like specific apps or docker images to larger disks. There is more information for that at https://docs.cloudron.io/storage/#disk-layout
@ghaisasadvait did you have any success with this approach? It is not really recommended at all of course, since I don't think that was ever tested. Still would be good to get some more information how it went.
I think we won't change the minimum requirement tested for in the cloudron-setup script for now. It seem quite the edge case to have that little storage available, however it is good that we know there is a possible workaround for those cases.