They can be played on their own though, because they have a warscroll just for them.
Regarding the changecut box, that would be my first choice however it's no longer available.
I will only get demons after 1000 pts and probably just horrors (or a lord of change if I get the money for it) so the starting box is not very interesting to me
Is the shadespire warband a decent starting to point for a Disciples of Tzeentch warband?
I was planning to start a 1000 pt Tzeench band with it and a box of acolytes, tzaangors, skyfires and maybe another hero.