1-Will it automatically get, or allow me to download the Oppo usb driver onto it?
The Id's use a Linux operating system, so if the DAC supports Linux, there is no need to download a driver. The Oppo UDP 205 appears to support Linux.
2-Since I've spent a fair amount of time 'tagging' my music on MC23 I don't want to have to do it all again. Will I be able to export my library (with all my tags) to it?
You can, but moving a library from Windows to an Id can be messy. I think an easier option is to use the Id purely as a renderer. In this case, you connect the Id to your network and the USB DAC. Just leave the external hard drive where it is (I assume it's connected to the laptop).
Once the Id is connected and powered on, boot the Id into GUI mode (option 1 in the main menu), or connect to it remotely. Then configure Media Center to output through the DAC the same way you would in Windows (Tools -> Options -> Audio). You will see a lot of choices for the audio device, so you might need to try a few different options. You should be able to tell which options are the USB DAC by the name. Try an option that begins with "hw:" first.
Then, from Media Center on your laptop, the Id will show up as a playback zone in the list on the left side. To play music to it, from Media Center on your laptop, right-click a file/album/playlist and select: Send To -> Play (<Whatever the Id name is, usually something like Id-XXXXXXXXXXXX>) -> Play.
3-You said I could open up 'Panel' in my web browser. Is that the similar to the GUI I see when I open MC23? Can I access 'Audio,Artists, playlists, etc. and choose what to play from there on my laptop? And control play/pause/skip, etc from my laptop?
Panel looks different than the Media Center interface, but it's made to be simple to use. There is nothing extra to download or install. It's a full interface, so you can play/pause/skip audio, images, and videos in your library, and you can run Panel on any device that has a web browser. You can find instructions for it here:
https://yabb.jriver.com/interact/index.php/topic,116687.msg806546.html#msg806546Can I control it from my laptop, but have all the files stored in the ID and have no hardwire connection between my laptop and the ID, but still control the playback from my laptop thru my network?
You don't need to have a hardwired connection between your laptop and the Id; however, the Id and your laptop need to be connected to your network to communicate, either by ethernet or WiFi.
4-Is there any advantage to having the built in 2TB storage over an external HD? Is that what you were referring to with the bandwidth issues?
First of all, the built in 2TB drive only comes with the IdNUC. The USB bandwidth issue is mainly for the IdPi, not the IdNUC.
To answer the question, kind of. There is an advantage to internal drives over USB drives. The internal drive uses SATA III which has more bandwidth, but you probably won't notice the difference, especially if the USB drive is USB 3.0.
That being said, if you decide to use the Id purely as a renderer, you won't need the 2TB built in drive.
5- Can it play DSD files or are they converted to PCM?
I think Awesome Donkey put it a lot better. It depends on what the DAC supports.