Sources on minyan?

I've promised my community I'll do a study session on minyan for Shavuot, particularly on why we need a minyan to say Kaddish. I know this stuff fairly well on a general level, and can probably put something together that will be informative and provoke discussion. But I don't have actual texts, and, well, I threw out all my Jewish learning notes when I downsized. Mainly because they were just in big disorganized piles taking up space and I wasn't that convinced I'd ever be able to find anything. When I say texts, I mean really basic stuff like the Mishnah.

Also, fellow Jewish educators, whether professional or informal, what's a sensible amount to charge for one-to-one BM tuition? The mother of the kid I'm working with is absolutely insisting on paying me in spite of my protests, and I want to give her a reasonable figure. Basically the lessons are half an hour to 45 minutes, with about the same amount of prep time. My best guess is somewhere around £20 per lesson, but I really don't know if that's way too low or way too high.