fwiw, one piece of fallout from listing the same address on a loopback
interface as a real iface is that ntpd 'listen on *' tries to listen to
the same address twice and fails, so you need to list the addresses
individually in ntpd.conf.
(other than that, I haven't seen any major problems, but I'd put it in
the category of "if you do this you'd better be ready to work out what's
breaking and how to fix it" and my third question definitely still