Besides that, pre-casting ES doesn't work.

In 1.09 at least, if you cast ES from an outside source without having any points in it and then lose those skill points, you won't actually get the damage converting effect, even though it shows the floating ball over your head.
I see no reason why this would have been changed in 1.10, so.
Edit : oh and also, my personal advice would be to get a fair amount of Mana. Mana is the source you thrive on, and if you don't have any or run out of it too fast, you can't make an effective dueler. The minimum for an Orb Sorc should be 1500, if you go beyond base ES, 1800+ is recommended.
I always played without CTA because I mainly played in private leagues and only take my character to public games when I'm bored or there are no league games up, and I consider CTA bad mannered because of the rules from where I play.
But with it you should have no problem getting that amount of Mana.
Once you have over 800 Orb damage, and you play in public Hell games, you shouldn't worry much about your damage. If people choose to absorb you, there's nothing you can't do about it with your cold spells, but if they don't have that kind of high Absorb, 8xx+ Orb damage is plenty.
Teleporting experience and practicing with aiming Orbs is the key, not a huge amount of damage or a massive Life pool, although both help of course.
Also, getting 8 FPC is by no means a necessity, 9 FPC is fast enough for alround play.
You Teleport a bit slower, but your damage will also be at least 20% higher, and you can enjoy the advantage of having full block which you might not if you go 8 FPC.
Playing experience, a good connection + computer, a steady Mana pool, damage, good items, is what makes a good Sorc in my opinion, and mostly in that order.