Migrating iTunes library when replacing the hard disk
The simple answer is iTunes has really only stores two types of data:


iOS backups
playlists, ratings, music, books, apps, movies, etc...


If you don't just want to plug in your iPad and other iOS devices and transfer purchases, then you'll want a $8 drive connector to connect your old drive as an external to bring over the media, the backups or both. Yu can also get these files from time machine or other backup (offsite or local)

Even after swapping the old drive, you can still start iTunes pointing to the old backup library and run / restore or export parts of the library playlists and move over just part of your library. 

It really depends on what exactly your setup involves (sync data over USB like calendars or photos) may require you to migrate some other data or watch/control the first sync to ensure your iPad doesn't lose unintended data.