In iTunes, on your first machine, you will have to go to File|Library|Export Library.
This will generate your Library.xml file.
If you take a look in it, you will see for each file all the fields you will find in iTunes (location on HDD, play count, rating, etc...).
Now, on your new machine, after having installed iTunes, you have to go to File|Library|Import Playlists (not obvious at first as I was looking at an Import Library menu but it doesn't exist) and select the xml file you exported on your first machine.
If you try, as I did first, to edit the xml file and overwrite the newly created one, when launching iTunes, it will delete it and create again an empty new one. You have to go through this Export/Import process (which is quite quick).
PS: you may have to edit the xml file anyway before importing, if the paths to the music files changed from your initial machine. For example, I upgraded from WinXP to Win7. As the user folder path changed, I then had to edit the paths c:\users and documents\myuser\My Documents\My music to c:\users\myuser\Music, or something like that, I don't remember exactly.
PPS: Always keep your exported xml file untouched somewhere until you have everything OK on your new machine...
This probably can be achieved by just using iTunes Match, don't know if you're willing to subscribe to this. The master library with AL is getting matched, giving you access to the AAC versions from the cloud. From then on, everything you do to a file in your AL library is getting automatically synced to the iCloud AAC version.
When you're on the go just switch to the local SSD library. Start with an empty library, activate iTunes Match and all your music get's visible without being physically on the device. You could then download all the AAC versions from iTunes or just those you want to have on the device. All changes between your master and this slave library should get synced, you just have to manually download music on your SSD when you add something new to your master library.
Best Answer
You can do all of these five (five because your second question is actually two separate questions) by subscribing to either iTunes Match or Apple Music service. How you do exactly any of those five, however, depends a bit on which macOS version your Mac is running on.