Why are you wanting to use the external drive is it so that you don't use up memory space on your laptop .
This is what I do , I use media player to rip the album to my pc , I then wait a while for media player to get album art and track information off the internet. NOTE … you say you want mp3 format so before ripping to pc open rip tab in media player and pull down options their is one for mp3. Next go to my music folder and right click the album you want and choose send to pen name.
EXTRA INFO.... some car units such as my wifes vw cant read album art so wont play the music so do this , in my music right click the albums art work and choose open , it will show a folder with the albums name on it , right click this one and choose send to pen name.