Looks like a fair set of rules, to be honest. I wasn't aware of the 'top posting' rule, though now that I think about it I've seen the inline commentary and the bottom- posting behavior on mailing lists that I've read in the past.
Luckily, neomutt+gpgme doesn't do inline signatures, but does do attachment signatures by default when you choose to sign a message (press p on the send/review screen). If you're using it to view a signed message, neomutt will attempt to verify the authenticity of the message by itself. It will "appear" inline because of neomutt+gpgme's behavior, but it is in fact an attachment. I'm not sure if the same things apply to vanilla mutt.