duplicate music files because of the type

I am trying to tidy up my itunes, I have duplicate files and want to make sure I don't delete the ones I need. I have an ipod and use a samsung phone to connect to my car with songs I have uploaded to google music. What is the best file type to keep? I am also wanting to upload cds to itunes but because my new mac doesn't have a drive I will have to upload via a laptop using windows and then put them on a flash drive and import to itunes, any help with this too please.

thank you