File transfer from Windows formatted HD to Mac formatted HD

Hi all, I have been searching the web in an effort to find an answer to this but thought it would be better to speak to you all. I have my music library (mainly FLAC) loaded on to WD or Seagate external hard drives which were originally formatted for Windows and are currently used with my Windows based Baetis Audio Music server in my main two channel system.

I am setting up a headphone system in my office and will use a MacBook Pro 2016 as server with Audionirvana. I will buy some new external hard drives for this system. My question is how can I copy the existing files I have on the Windows formatted HDs to the new HDs that need to be formatted for Mac?

I understand that Mac can read a Windows formatted HD but not write to it and I will need to write to these files as well. Should I first copy the files across to the new HDs and then after that re-format the HDs for Mac? Can I reformat after transferring my music or will it corrupt the files?

Thanks

James