Hi Stefan. Yes this is the iTunes for Mac forum, but sometimes questions end up in the wrong place or there is some crossover. You should be able to relocate the MobileSync/Backup folder using a junction as described elsewhere. As a PC user I don't have all the answers for this aspect for Mac users. Regarding the library itself however...
Here are typical layouts for the iTunes folders:
However in your case it would appear that your library has ended up in the ~Music folder instead of ~Music/iTunes.
If you have upgraded from version 8 (or earlier) to iTunes 9 (or later) at some point, then your media folder (everything inside the red outline) may still be called iTunes Music instead of iTunes Media. The extra Music folder inside the media folder is used if you have allowed iTunes to Upgrade to iTunes Media Organization (iTunes 9) or used File > Library > Organize Library > Reorganize files in the folder "<Media Folder>" (iTunes 10). Depending on your choices for Keep iTunes Media folder organized and Copy files to iTunes Media folder when adding to library plus a little bug in which one build changed the name of the file storing the choice of layout it is quite easy for some of your files to be organized according to one layout and some the other.
Assuming you're happy letting iTunes organize your files the following steps should tidy things up:
1. Make sure that under Edit > Preferences > Advanced tab your media folder is given as ~Music/iTunes Media. Edit if necessary, but don't consolidate files at this stage if prompted.
2. Select File > Library > Organize Library... > Tick Reorganize files in the folder "iTunes Media" and click OK. Skip if this option is greyed out (already upgraded).
3. Select File > Library > Organize Library... > Tick Consolidate files and click OK. This will bring any files currently organised outside the designated media folder into it. NB This will create duplicate copies of any file that needs to be consolidated, and you will need to manually clean up afterwards. If space is at a premium use something like Move Files to Folder to move files into the correct folders.
4. Select Edit > Preferences > Advanced tab, uncheck Keep iTunes Media folder organized and click OK.
5. Select Edit > Preferences > Advanced tab, check Keep iTunes Media folder organized and click OK. This triggers iTunes into reorganizing everything into the correct, portable, layout.
6. Close iTunes, wait a few seconds for it to finishing saving the library, then copy the entire Music folder to the root of the internal hard drive.
7. Rename the copied folder as iTunes
8. Click the icon to launch iTunes and immediately press down Option and continue to hold down until asked to Create or Choose a library. Choose the new copy of the library on the internal hard drive.
9. Once you are satisfied all is well you can delete the old copy on the SSD.
tt2