So with the new respec system, it will be easier for characters to get through lower difficulties since theres no need to save your skill or stat points anymore.
This opens up a whole new world to character development. You can dump your points into a low level skill that will own through Normal, respec in NM or Hell, then finish off with whatever you designate the character to do end game.
For a sorceress, I was thinking of doing a charged boltress through normal, respec to orbitaller in NM, then maybe finish off with a pure blizz for boss running.
There's no need for so much respecing. Save a couple for equipment changes.
Fire is less mana hungry but honestly mana still won't be as huge an issue as before since you can pump early points into energy. The games are all going to be crowded so you'll be leveling fast.
Whatever the build I'd pump most of the stats of the first 5 levels into energy. Just make sure you can wear breastplate (strength 30) when you hit act 2 so you can buy 3 open socket breastplate there.
If you go fire first just put a point into warmth and the rest into firebolt (it has a low mana cost) until you can get fireball then pump fireball as much as your mana can handle. Fire has the additional advantage of the leaf staff since you could shop for a 2os fireball staff in act 2 (or even act 1) to make leaf out of.
But you could go cold at first too, and that would get you to level 24 with blizzard partially synergized already. Then you won't want to respec until MUCH later to recover those stat points you put into energy. Meanwhile you'll have a nice blizzard going early on. Ice bolt, ice blast, and glacial spike are all synergies for blizzard so you'd want to juggle those till you got blizzard to keep your mana issues in check. I think you can easily go with those till level 24 when you get blizzard and having glacial spike for baal runs will make them easy.
I would go with firebolt/fireball/meteor/fire mastery as those own early on. 1pt warmth, and put 3 str/2 energy per level till you can wear a breastplate, then 3vita/2 energy till level 30ish as that will keep your mana going. once you can wear a 3os bp, stuff it with whatever sapphires you can find (perfs would be best). if you have 3 psaphire armor, then you can forego energy altogether and do full vit till you reach nm.