Atronarch is a much better ultimate IMO.

I think you would do better with light armor, the passives synergize much better if you are playing as a caster.

I use about the same rotation you do, but have light armor. I only cast crystal fragments when I get blue hands (forget the name of the proc).

I also have resto staff as my secondary weapon, and I keep a hot going on myself pretty much nonstop on every fight.

I use the twilight matriarch morphed for magicka regen, that seems to make a difference. Between that and the magicka return on endless fury, I seldom end a fight with less then 50% magicka. I'm often full magicka even after a group of 3.

Aoe is tough until you get destro staff maxed so you have the good magicka return on every kill. Impulse when you first get it will drain a lot of mana. That was my experience on my DK. My Sorc is level 33 doesn't have it maxed yet.

I've been leveling up destro staff and bow, hoping to have them both maxed by the time I hit 50. It sucks to level up a new weapon as veteran.

I use a Sword and Shield and Restoration Staff as my weapons and have found two different strategies for taking on multiple enemies in solo PvE.

Using the Sword and Shield to tank I find using Thundering Presence, Liquid Lightning and Critical Surge (with magelight for crit %) works well. Most opponents fall down while I mostly just block. Obviously you need to make sure you are close enough to damage the enemy so ranged opponents need to take priority as everyone else should just follow you around. It may not be the quickest way to kill but it seems to do the job.

If you are trying to stay at range Encase morphed to snare is a must. Use Daedric Curse then encase the enemies once they get close, the AoE of the curse should help burn down other targets. Use Mage's Fury once the target hits low health for another AoE and you can always use liquid lightning straight after an encase to increase AoE damage.

Of course Crystal Shards is a useful tool for any ranged build but save it for when it procs. If I am between curses and Shards hasn't procced the restoration staff heavy is a handy tool for mana regen while hopefully ticking health low enough to set off the Mage's Fury AoE.

I play a melee sorc using dual wield abilities and stormcalling, with a secondary resto staff. Thundering presence is an insane defense buff as well as constant AE damage, I try to keep it running constantly.

For multi mob pulls this is what I usually do:

Cast Rapid Regeneration pre-pull then swap weapons.
Activate Thundering Presence and dot up all 3 mobs using Blood Craze from dual wield.

Then I use Rapid Strikes to get the healing/support mob to execute range and use Mage's Wrath for some extra splash damage. By then they are low enough that I can port through them a couple times with Streak to finish them off.

To take all 3 down more evenly you could use Liquid Lightning or Whirling Blades instead of Rapid Strikes, but the basic idea is the same. Your Mage's Fury will do a bit less splash damage too since you morphed it for the mana return.

I also use overload, but I tend to build up to 1000 ultimate and sit on it unless I really need the massive AE or very efficient ST damage. I like to abuse the fact that it is a toggle ability.

If I absolutely don't want to deal with the mobs and just want them out of my way: Thundering Presence, Liquid Lightning, Overload heavy attack. Where did all the mobs go?!

For reference, I am level 39 and an even split between magicka and stamina points. I wear 5 pieces of light armor and 2 pieces of Medium.

And yes, Surge works on your weapon abilities, not just light and heavy attacks.