Theoretically, you need 10 men in the same room in the same service. That's the tradition. Remember that a minyan is really a rabbinical decree; there's nothing in the Torah about how many and for what. The idea of a minyan is derived from the phrase in the Torah that the "children of Israel will sanctify the Lord". Why ten and not two or three? It's the rabbinical exegesis of the phrase along with the idea of a congregation. These days, things have become more progressive. Now it's ten adults and women are counted.
A former religious leader of our community said he'd do a Mourner's Kaddish with only six, because you can continue praying the reader's repetition of the Amidah if you start out with ten and four leave (again, rabbinical). For me, I'll do a Mourner's Kaddish even if there's only a few people because for me it's more important that people honor their loved ones. With the coronavirus, we've used the virtual audience as a minyan.
It's probably a given that the Conservative and Reform movements will allow it while the Orthodox would probably tell you to just pray on your own and do what you can do. In my view, the important thing is community so rabbis like me are willing to relax the halachah to accommodate the extraordinary.
And yes, Conservative Judaism counts a Torah as one since when it's beyond repair, they bury it like a person.