Can I remove original music file after imported into iTunes w/ copy enabled
Yes - unless there is something wrong with iTunes and it didn't copy the song, you can delete these second copies of songs.

I would use spotlight to check before you delete things until you gain confidence that the copy is working as designed. In the long run, it will be faster to let iTunes move the files so you don't need to clean things up.

Also, a good Time Machine backup can help if you accidentally delete too much.