MASSIVE!!! (just kidding)
The Musiah piano lesson course is divided into 13 levels. As each level is completed, the next level is downloaded.
The initial download file is the app itself at around 57MB for the Windows version, 74MB for the Mac version and 117MB for the iPad version.
Then, straight after installation, the app will start downloading content files for the first level of lessons, virtual instruments, backing tracks, music manuscripts, etc. totalling around 665MB.
Level 1 has more data than subsequent levels. Later levels are smaller to download, ranging from 40MB to 90MB.
The total course content (all 13 levels) equates to 1380MB, plus the initial app itself as indicated above.