The one thing that I don't like is that it utilizes a proprietary file format. This isn't an issue with daily use but is going to make the current upgrade (drive size) process more difficult. I will first need to copy everything over to another drive, replace the NAS drives and copy back. Audio files are already backed up elsewhere, but will need to do the same for movies.
I would suggest setting up for RAID 1 (redundancy) and not go excessive on storage space. 2TB has been serving me well for six years, currently have ~1TB audio (mostly 16/44.1 FLAC with some HD) and close to 1TB of movies (these don't really need to reside there all the time but it's convenient). I will probably just upgrade to 4TB, may consider 8TB depending on drive deals. Drives have a lifespan (I am likely pushing it at six years), so paying for unused storage could end up being a waste.
As far as MAC goes I can't help you out, I am a Windows PC guy but am sure plenty utilize the WD My Cloud without issues. And for software, I wrote my own PC & iOS (iPhone) app for playback & remote control.