Canonical Support and Services will support you to some extent on all of these questions through our Ubuntu Advantage program, but there are some caveats:
A1. Wine is in the Universe repository, not Main, and is therefore technically "unsupported". What that really means is that there are no guarantees that we can solve the problem or provide a patch. We will, however, give it a good effort and assist in configuration questions and triaging the problem. We have some really great support engineers but if it's not in Main, there are limits.
A2. Similarly, by definition PPAs are not part of the Main repository. In some of the examples you've cited, there are suported packages for those apps in Main (e.g. libreoffice, openshot) so in such cases we would like to see if the same problem can be reproduced in the mainline Ubuntu version of the package. You might use the PPA version of openshot, but if the same crash/bug exists in the mainline Ubuntu version, then there's no problem. It will be supported. However, if it results in a patch, we're going to push that fix into our packages in Main. Getting the same patch into the PPA which you use would take some coordination with the PPA maintainer and is not guaranteed at all. If that PPA is maintained by a Canonical employee, an Ubuntu member, or the package's upstream maintainter, then there is a decent chance, but again, no
guarantee as these are not the offical Ubuntu archives or our Canonical Support PPAs.
A3. That's a broad question. There are server-side email migrations and then there are client-side migrations. Either way, it seems to me that this type of issue would not fall under Support but Services (i.e. consulting). I would contact Canonical Sales and ask for an evaluation.
Since you asked for details, let me add that there are several different types of Ubuntu Advantage subscription: desktop, 3 levels of server support (essential, standard, advanced), cloud guest, and cloud infrastructure. Each choice comes with a client subscription for Landscape, our system management console.
And you're only obligated to subscribe the systems that you think require support. Every other system (test, dev, uat, etc.) can run the exact same distribution as your supported systems.
Good luck, I hope we can help!