So, suddenly it's useful to bind all the spells? Why aren't you QQing about Renew and GH? You should make sure he doesn't bind those spells and becomes a fail priest
"Open your spell book now either keybind or place every single spell some where and I mean every single one except stuff like lesser heal and heal and stuff like thatofc. Because it might not be often but every single spell can be usefull! You might never use it but having it avalible when you need it is alot better then not having it the 99,9% of the time."
Is a great advice, and something I agree any player of any class should do. Using that obscure spell when the time is right might make a difference once in a while; and that's what matters.
I would advice stacking on Intellect a lot as well when starting out with Discipline, it gives more room for mistake while you still learn the healing style (and develop your own healing style) - eventually you'll find that you don't even go under 90% mana during heroics, or you barely every get low on mana in raids (Except if things go bad of course), then you know it's time to start leaning more towards Spellpower.
Basically; Get enough mana/regen until you feel safe healing, i.e. you're not worried about going OOM - when you're at that point, Spellpower becomes great because that's what actually keeps people alive.