Then there is 3 discs and what is labeled chapter 1 starts where? I mean what am I missing? Also is it easily found or really hard to find the music album? of course I mean by internet means.

The sequence properly runs "Rhea, Earth Chapter 1, Earth Chapter 2, Earth Chapter 3".
The only source I can suggest (beyond, of course, LDDb) is Yahoo Japan Auctions. I bought a lot of Gall Force discs to get the music-video album. I don't know how common it is, although I have the impression that they were usually struck in smaller quantities than the movies — one possible exception being the Tenchi Sound File, which exists in both Pioneer & Sony pressings.