I'm no great wizard, but I'm learning (and liking) Elec/, so I'll reply. 
1. Get Gloom for your ST DPS, sure, but forego Dark Oblit (/EM has plenty of AoE) and get Build Up instead.
2. Weigh Darkest Night versus Manuevers depending upon your playstyle. Darkest Night gives the biggest solo bang for the pick, but higher-level enemies and such will resist its effects, plus you have to keep recasting it.
3. Especially since your getting Power Surge for "oh crap" moments, weigh Spiritual vs Cardiac for your Alpha Incarnate. Due to Power Sink, the +Rech from Spiritual may outweigh the EndRedx from Cardiac. If you get perma-Energize, you get to constantly stack its +Regen with Spiritual's +Heal effect on Regen, and this just might outweigh Cardiac's +ResDam. Be careful here though - the ResDam helps with against enemy alphas better, whereas both ResDam and Regen help against sustained damage.
For slotting, I would sacrifice some Rg/AoE/E/N defense for more S/L defense, and swap the Scirocco's Dervish in Thunder Strike for five Obliterations. The Accuracy of Charged Brawl and Lightning Field could use some help as well - if you can put one more slot in Weave (LotG) or Lightning Field (with Oblits) it'll help - just watch the "rule of 5" when making changes, as you're near it for both +5% Rech and +9% Acc now.
Current primary characters, all on Guardian:
The Amber Fist (Elec/Stone Tanker) | Pixelbeater (Fire/Kin Corr) | The Sequencer (Bots/Traps MM)
Blakkat (Claws/Dark Brute) | Mhogus'thra (Ill/Dark Cont) | Wyldhunt (Beast/Dark MM)
What diff do u solo at? Id keep most of your stuff as is and go for perma haste, which brings you to almost perma energize. That will allow you to get nerve alpha instead of cardiac a which will buff your ACC and defense. Since you are one purp insp from softcap that will do you better in the long run. Remeber energize gives a 37% end discount... Better than cardiac. If you can slot the glad wall +3%res to make up for the cardiac t2+ res buff. Your toon should be pretty tank by then 
I dont really know what to say
Electric Armour and the Soft cap
Electric Armour and the 1st 20 levels
Thundra Knight
click here for You want the best TANK!? I'll let you decicde!
It seems like more common builds a Ela/SS and Shield/Elm, but I like thematic builds. I'm currently building for moderate defense and recharge. I know that it is usually more efficient, to focus on one area, but I enjoy having a will-rounded character. I'm currently planning on no purples/PVP IOs, but if budget allows I am not adverse to adding them.
Hero Plan by Mids' Hero Designer 1.93
http://www.cohplanner.com/
Click this DataLink to open the build!
Shortt Circuit: Level 50 Science Tanker
Primary Power Set: Electric Armor
Secondary Power Set: Electrical Melee
Power Pool: Leaping
Power Pool: Fighting
Power Pool: Speed
Ancillary Pool: Soul Mastery
Hero Profile:
Level 1: Charged Armor -- RctvArm-ResDam/EndRdx/Rchg(A), RctvArm-ResDam(3), RctvArm-ResDam/Rchg(3), RctvArm-ResDam/EndRdx(34)
Level 1: Charged Brawl -- KntkC'bat-Acc/Dmg(A), KntkC'bat-Dmg/EndRdx(7), KntkC'bat-Dmg/Rchg(7), KntkC'bat-Dmg/EndRdx/Rchg(9)
Level 2: Conductive Shield -- RctvArm-ResDam/EndRdx(A), RctvArm-ResDam/Rchg(5), RctvArm-ResDam/EndRdx/Rchg(5), RctvArm-ResDam(9)
Level 4: Jacobs Ladder -- Oblit-%Dam(A), Oblit-Dmg/Rchg(11), Oblit-Acc/Dmg/EndRdx/Rchg(11), Oblit-Acc/Rchg(13), Oblit-Dmg(13), Oblit-Acc/Dmg/Rchg(34)
Level 6: Static Shield -- Aegis-ResDam(A), Aegis-ResDam/EndRdx(21), Aegis-ResDam/Rchg(31)
Level 8: Grounded -- S'fstPrt-ResDam/Def+(A)
Level 10: Combat Jumping -- LkGmblr-Rchg+(A), LkGmblr-Def(37), Ksmt-ToHit+(43)
Level 12: Energize -- Dct'dW-EndRdx/Rchg(A), Dct'dW-Rchg(15), Dct'dW-Heal/Rchg(27), Dct'dW-Heal/EndRdx/Rchg(29), Dct'dW-Heal(29)
Level 14: Super Jump -- Zephyr-Travel(A), Zephyr-Travel/EndRdx(15)
Level 16: Thunder Strike -- Sciroc-Acc/Dmg(A), Sciroc-Dmg/Rchg(17), Sciroc-Acc/Dmg/EndRdx(17), Sciroc-Dmg/EndRdx(19), Sciroc-Dam%(19), FrcFbk-Rechg%(21)
Level 18: Lightning Field -- Erad-Dmg(A), Erad-Dmg/Rchg(23), Erad-Acc/Dmg/EndRdx/Rchg(23), Erad-%Dam(27)
Level 20: Lightning Reflexes -- Run-I(A)
Level 22: Boxing -- C'ngImp-Dmg/Rchg(A)
Level 24: Tough -- RctvArm-ResDam/EndRdx(A), RctvArm-ResDam/Rchg(25), RctvArm-ResDam/EndRdx/Rchg(25), RctvArm-ResDam(40)
Level 26: Power Sink -- Efficacy-EndMod(A), Efficacy-EndMod/Acc(36), Efficacy-EndMod/Rchg(42), Efficacy-EndMod/Acc/Rchg(42), Efficacy-EndMod/EndRdx(46), Efficacy-Acc/Rchg(48)
Level 28: Chain Induction -- Mako-Acc/Dmg(A), Mako-Dmg/EndRdx(31), Mako-Dmg/Rchg(36), Mako-Acc/EndRdx/Rchg(42), Mako-Acc/Dmg/EndRdx/Rchg(43), Mako-Dam%(43)
Level 30: Weave -- LkGmblr-Def(A), LkGmblr-Def/EndRdx(31), LkGmblr-Rchg+(33)
Level 32: Taunt -- Mocking-Taunt(A), Mocking-Taunt/Rchg(33), Mocking-Taunt/Rchg/Rng(33), Mocking-Acc/Rchg(34), Mocking-Taunt/Rng(37), Mocking-Rchg(37)
Level 35: Hasten -- RechRdx-I(A), RechRdx-I(36)
Level 38: Lightning Rod -- Oblit-Dmg(A), Oblit-Acc/Rchg(39), Oblit-Dmg/Rchg(39), Oblit-Acc/Dmg/Rchg(39), Oblit-Acc/Dmg/EndRdx/Rchg(40), Oblit-%Dam(40)
Level 41: Gloom -- Thundr-Acc/Dmg(A), Thundr-Dmg/Rchg(45), Thundr-Acc/Dmg/Rchg(45)
Level 44: Dark Obliteration -- Posi-Acc/Dmg(A), Posi-Dmg/Rchg(48), Posi-Acc/Dmg/EndRdx(48), Posi-Dmg/EndRdx(50), Posi-Dam%(50)
Level 47: Darkest Night -- DarkWD-ToHitDeb(A), DarkWD-ToHitDeb/Rchg(50)
Level 49: Power Surge -- RechRdx-I(A)
Level 50: Cardiac Core Paragon
Level 0: Freedom Phalanx Reserve
Level 0: Portal Jockey
Level 0: Task Force Commander
Level 0: The Atlas Medallion
------------
Level 1: Brawl -- Empty(A)
Level 1: Gauntlet
Level 1: Sprint -- Empty(A)
Level 2: Rest -- Empty(A)
Level 4: Ninja Run
Level 2: Swift -- Run-I(A)
Level 2: Health -- Numna-Heal(A), Numna-Regen/Rcvry+(46), RgnTis-Regen+(46)
Level 2: Hurdle -- Jump-I(A)
Level 2: Stamina -- P'Shift-EndMod(A), P'Shift-End%(45)
1) haste or Build-Up? I'm not up to Perma-Haste, but I do have it with about 20 sec downtime, which is good enough for me. I'm just not sure which will improve overall DPS. I primarily solo for now, so DPS is important.
2) Soul or Mu or None for APP/PPP? I like the idea of Soul for another damage type, but Mu appeals to my need for consistent theme. On the other hand, if I skip the APP/PPP completely, I can pick up Leadership which should bring me to 32.5 def all and completely Perm hasten, along with freeing up a few more slots.
So, great wizards to the tanking world, what say you to a first-time tank who is so far enjoying the experience. :-)