Q: how do i transfer my itunes to my new mac without losing all the music i didn't purchase on itunes

Just copy your iTunes folder from your old Mac to the new Mac.

Copy your ~/Music/iTunes folder to an external drive that will hold all the files. WIthin the iTunes folder is an iTunes Music folder which has all your songs.

Take care to consolidate your itunes library first so that the library has a copy of all your music IN the library and not just referencing music in other folders.

90% of my itunes library is ripped from CDs

If you copy the entire folder, everything will transfer, including the iTunes appearance, i.e., playlists, folders, podcasts, etc.