MP3Tag is by far the best tagger I've used for for any platform. I also have licenses for Tag&Rename and a few others that I don't use at all anymore. It's the most complete and can easily find problem tags. I make sure to always delete ALL tag data except ID3v2.3 and I also use its "Extended Tags" to make sure nothing unexpected is set by accident.

I use it in combination with iTunes for all my tagging. First iTunes and then MP3Tag.

In iTunes, since I'm on a Mac, I use a ton of AppleScripts to do things that you can't do natively in iTunes UI for tag manipulation - some of these things you can do in MP3Tag as well.

iTunes will deal with multiple discs as part of a single release properly as long as the correct fields are filled in. Make sure both the disc number and "of disc" fields are populated. Example in the Get Info window: 1 of 2

When you list the collection in iTunes and sort using "ALBUM by ARTIST -> YEAR," it will display the album with disc 1 first and then disc 2 following it. Example screenshot below.

I don't know how this appears on the new Nano. Older iPods in the classic line had terrible software and it didn't even use the Album Artist tag, even though all that was long ago supported in iTunes. I would think the Nano would deal with everything iTunes can do, but it may not.