Neat! I can help with some parts:

How many members are there on ScuttleButt?

This will always be a difficult number to measure, it'll have to be through statistical census in the future. The exact number will always be impossible to measure because of decentralization. Right now I think we're in the range of a few thousand, maybe ~5 thousand? The way I know this is that you can check the number of ids in your local database and extrapolate a bit. I know e.g. that Dominic has 1000+ followers on SSB, and I'd suppose most people would follow him. So SSB is at least 1000 or so, but probably a bit higher, so I'd say thousands.

Is there a charted/logged growth curve?

https://celehner.com/ssbc/stats/daily.html

But remember, this only reflects a portion of the whole SSB community.

How long has ScuttleButt existed?

Exactly 4 years! https://github.com/ssbc/secure-scuttlebutt/commit/d8420a185439587990c8b752780096e3f6373c28

We need at least two more people, who?

Add @mix, because we need to mix him in

Do we want to add more projects examples beyond...

Well, Patchwork obviously. Also TickTack because it looks crispy and juicy.