Sprit is secondary when it comes to raiding.

Spirit is KING when it comes to leveling. However, there still has to be a balance between damage and spirit. But due to lack of nice +dmg or +shadowdmg items pre level 70, spirit would be easier to obtain. However, you have to make sure that you have spirit tap when you level and you're all good to go.

The other questions have been pretty much covered by others, but if you want some pointers for raiding just let know and I can give you my prepatch 2.3 experience as a shadowpriest. Dont think there has been much changes to them, but I've been off touch with WoW for a few months already, pretty busy with other stuff.