So, you've had a sennight to mull over your own answers to these questions.

Here are mine.

What's the minimum number needed for a coven?

Traditionally, three.

“It takes three witches to make a coven; two witches is just an argument” (Terry Pratchett).

This seems reasonable to me.

Is there a maximum number?

Yes.

If so, what is it?

Well, we might as well go with tradition and say thirteen here, although I suspect that being so large would strain the boundaries of personal intimacy and small-group dynamic that a coven requires.

I've heard of “covens” with up to 150 members. By my lights, this pushes the concept of coven to the point of meaninglessness.

Let me be uncharitable and call such groups mega-covens.

Does a coven actually need to meet?

Yes.

If so, how often does a coven need to meet? Once a month? Once a year?

Let me say here, regularly. Individual groups will best determine what's regular for them. The Warlocks of the Driftless get together 3-4 times a year, and we seem to be a coven-in-the-making.

I'd say, Once a year, minimum.

Do on-line meetings count...?

No.

...or do they need to be real-world, physical get-togethers?

Yes. Call me a dinosaur, but an on-line coven is not the same entity as a real-world coven. I won't say that it's not a coven at all, but that it is at best an on-line coven.

How long can a coven go without meeting before it ceases to exist?

Let's be traditional and say, A year and a day.

How long does a coven need to exist in order to properly constitute a coven?

Let's be traditional and say, A year and a day.

Does a coven need to perform ritual together?

Yes. Otherwise it's just a social group.

Does a coven need to work magic together?

Yes. Otherwise it's just a social group.

If a coven meets “on the astral,” does that count as a meeting?

If the coven is a regularly-constituted coven that occasionally meets “on the astral,” I would say yes. As an entity, though, an astral coven is not the same as a regularly-constituted, “real-world” coven.

What constitutes continuity of identity in a coven?

Shared awareness of continuity.

When all the original members of a coven have died or otherwise departed, can it be said to be the same coven?

If there's an ongoing and shared sense of continuity, yes.

If a coven goes out of existence, and then re-forms, is it the same coven or a different coven?

You'd have to ask the coven.

Can you belong to more than one coven?

Yes, although in Paganistani courts such behavior constitutes valid evidence of mental instability, if not actual insanity.

Can a nuclear family be a coven?

Normally, no. A working couple and their child or children is different from a coven.

I could imagine circumstances—persecution, say—in which this might not be the case. But even then, this seems to me a stopgap situation, far from optimal.

My friend and coven-sib Magenta Griffith suggests that such a coven might be in danger of “spiritual inbreeding.”

Her choice of language here strikes me as significant; I suspect that the general prohibitions against incest might well be operative in such a situation as well.

Can non-witches constitute a coven?

Only metaphorically.