Ok, so I went ahead and installed a buddypress site,as per instructions!
Everything went more or less well. First I tried the BP 2010 child theme and that just didn’t seem to work. The menu items all showed up in plain text below the page. So I went for the the default BP theme.
The only quibble I have at the moment is that Is et up a second profile field group and it doesn’t show up in edit profile. Am I missing something?