regard to the siyum for the fast of the first-born
With regard to the siyum for the fast of the first-born, it is possible to participate in a siyum via zoom, and there is no halakhic option to say Kaddish after the siyum.
As for saying Hallel, there is a controversy regarding saying Hallel on Pesach night, if it can be said by an individual, and whether it can be said with a bracha. Rabbi Riskin says that one can say Hallel with a bracha.
Saying Tefila Tal - Under usual circumstances, one should only recite Tefilat Tal after the public has already said this tefila.
Now that there are no minyanim, everyone will say this Tefila when they get to Musaf.
May the merit of all of our individual prayers allow us to eat from the special sacrifices soon.
HaRav Shlomo Riskin, Mara D'atra
HaRav Eytan Weisz, Secretary of the Religious Council