Very good points so far.
Im going to try to give you an idea of your fear
“if it will be enough dakka”
At +10 skills from Gear and
the very wise advice given to max Firebolt, Fireball and Mastery.
A Fireball does
2259–2608 a fireball against a target dummy.
My enchantresses Explosion Arrow does
1655–2114 against a target dummy.
Most of the time on single or until players 2-3.
Your limiting factor on non fire immunes will be overhit.
And the lack of pierce.
Might need a few for a Batch of cows but nothing u cant manage with that sorta fcr.
Id +1 on Blizzard vs Orb.
Just take what you enjoy more and complements YOU playstile.
Technically Orb needs less to max.
But that doesnt mean same invest in Blizz isnt serious enough dakka.
Enjoy your Sorc 
Cheers