You've got a lot of questions/issues going on here, but I'll try to make sure I answer them. First, I want to acknowledge that the Sony PRS devices are the most delicate (read temperamental) of ebook readers. As you have likely discovered, Sony is one of the devices that does not play nicely with Adobe Digital Editions. If you want to get public library ebooks on a Sony PRST2H you can download directly (video instruction), or titles can be transferred using Sony Reader Software (but not in ADE).
BEFORE you try to uninstall everything to reinstall and fix, I suggest you try the following:
For Sony PRST2H:
2. Download Sony Reader Software to computer.
3. Authorize Sony with Adobe ID using Sony Reader Store software. For steps, see video. (Skip video to 1:30)
(Side note: Use the de-authorize steps from the video to remove Adobe ID from your old, broken Sony.)
4. Attempt to download directly EPUB ebook from your public library as a test.
Hopefully this resolves your problem with the Sony. If not, and you just want the answers to your questions, here are my answers:
*Software conflicts: I am not aware of Kobo & Sony software conflicts. Nor have I heard of this before. That said, may be conflicts
*Keyboard commands: The most important keyboard command for devices is CTRL + SHIFT + E (or Command +SHIFT + E on a MAC.) The CTRL + SHIFT + D command you mentioned is for de-authorizing ADE, while CTRL + SHIFT + E is for devices. If you want to remove an Adobe ID from your Kobo for some kind of fresh start you will want to plug in your Kobo, open ADE, and press CTRL + SHIFT + E. (Your Sony uses slightly different steps as I already said.)
From testing, the keyboard commands on ADE 1.7 are exactly the same in 2.0. One thing I like about ADE 2.0 is that it comes with an ebook userguide upon install that lists every single command. Most are pointless. One of the main difference (important to me) is ADE 2.0 is that you get an option to deauthorize right from your widget menu options which is VERY useful in my opinion. The one thing I miss about the latest version of ADE 1.7 is that it was dummy-proof in that it forced you to add an Adobe ID first time you opened it.
Hope this helps.