If I do not have the music stored on a hard drive anymore (or simply on an external hard drive) will iTunes Match still work? For one year? As long as I pay the annual charge?
Yes, it will. It has been flakey over the years, with some songs refusing to download, but it has been pretty stable lately. I love it. But I still keep an offline archive.
edit: I also keep songs on google music. it allows downloads and is free for about 20k songs.
Thank you.
Also - The same goes for iCloud Drive. Do you need to have the files constantly syncing to a hard drive, or can I put my iPhoto collection on iCloud Drive, sell my iMac, and remotely access the files in the cloud as I would be able to with DropBox.
Essentially, are they basically the same service?
Yes, it is not a SYNC service, so you can delete the local copy and the iCloud copy will remain. I use it sparingly, it works like dropbox. I don't trust the reliability aspects (of any cloud service...use it as a backup, not the only copy), but I trust the privacy aspect of iCloud more than dropbox.
iCloud Photo Library, on the other hand, is a SYNC service. Delete the local photo, it deletes the cloud copy also.