Does watching forbidden things and moving the private parts to the point of masturbation during the daytime in Ramadan necessitate both a make-up fast and expiation, along with repentance? And what is the obligatory expiation in this case?

One must repent to Allah Almighty for intentionally looking at forbidden scenes and for illicitly arousing desires, as well as for invalidating an obligatory fast and violating the sanctity of the blessed month. That day must be made up for, but the severe expiation is not required, as it is only obligatory for intercourse.