Answering all questions one by one.
- Are you sure you need all 5 dvds? If you are about to install it to a pc with slow or no internet connection, then go ahead and buy them.
If not, download the relevant installation iso, burn it on a disk, boot with it, install debian and download the packages you need from the repos.
- Yes, although I have never used either of them.
- Yes, that's how my setup is.
- Yes and no, depending on the application you want to run in wine.
- If latest and greatest is what you want, you should better look in testing and unstable branches. They contain a little more stuff than stable and in more recent versions. Of course, stuff that got deprecated since debian stable was released, eg kde 3.5.10, cannot be found there.
- Mint was ubuntu based since it first started and now they are making an attempt to switch to debian (testing) based in order to get it as a rolling release.