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You're on the right track as far as showing users the PC versions of pages without an equivalent instead of the 404's: "If your content is not available in a smartphone-friendly format, serve the desktop page instead." -http://googlewebmastercentral.blogspot.ca/2013/06/changes-in-rankings-of-smartphone_11.html However, you should let Googlebot (mobile or not) crawl your site the same way as your users would, which means you shouldn't block googlebot-mobile. It is totally fine for a desktop page to be ranked in the mobile index. It's not ideal (see article above) but it's better than not being there at all. Think about it this way: if you're OK with your mobile users to see non-mobile-optimised pages, then it doesn't matter whether they come from Google or not. The page is still relevent to them. As an extra, you could consider making some of the non-optimised pages responsive such as to make the user experience a bit better. Sometimes a few tweaks here and there can make a difference.

Answer to First question: I don't think anybody knows yet as Disavow just hasn't been around long enough yet. But what I read is that it causes Follow links from the "bad" domains to list to be considered NoFollow links and therefore harmless. Answer to Second question: Yes, yes, and no.  I wrote about this in another posting yesterday here: http://moz.com/community/q/google-disavow-file-update Good luck!

Days, weeks, months, or sometimes never It is a very inexact science, and we're unaware of the vast majority of the 500+ updates Google makes every year.