OK, so it turns out (probably unsurprisingly) that it’s a lot more complicated than I was hoping for! I’m a complicate “newbie” and just editing a few videos for home, so I guess as long as I get something “about right”, that’s good enough.
I used a combination of the “Normalize” switch (the Normalize Peak Level in preferences defaults to -0.1) and audio event envelopes. When I play it, the meters on the surround master max out at -0.1 (only momentarily) and probably average at around -12. Most importantly to me, it sounds OK without me having to adjust my speakers.
Thanks for your help.
p.s. I don’t suppose there are any good links to “beginners guides” to this kind of thing (or video editing in general)?