s: on zh-classical.wikipedia.org should be changed zh.wikisource.org because ancient articles are also saved there. zh-classical.wikisource.org doesn't exist and is not needed.
Maybe b:, q:, v:, n:, voy: should be changed too. But I'm not sure. As a classical language, there won't be any "news"?
Cannot be done IMHO. Those are the global interwiki prefixes working for
700+ projects defined in the interwiki map. I think it is easier to teach
users to use s:zh: instead.
Yes. It is useful when you need to use iw link in mass announcement in village pumps for example. Otherwise you must send one message per language. Or when you just need to inform community about something you really want same interwiki map as you do not need to ensure links are correct.
Hmm. Not exactly same but it work the same way (at Wikipedia :de is for dewiki, at Wikisource for dewikisource etc). But :w:de is everytime dewiki.