Mace Mastery
Question 1: You must be a full villain(or rogue, not vigilante) to do the patron arc.
Question 2: I dunno.
Electric armor is resistance based and scorpion shield is defense based. All depends on what you want to build for.
Web Envelope is AoE and, I think, Electric Fence is single target. I'm not positive on this one though.
Yes, Electric Fence is single target, but it's not available to Corruptors, iirc.
I chose electric fence as one of my powers during my respec. I put two Gravitational Hold enhancements on it and it locks down Rom/Nictus in the ITF. Very cool for keeping him out of melee range for me.
Whoops. I was only reading the Patrons, thinking Mu Mastery. Silly me. :P
You won't need to do a respec and actually TAKE any powers from the patron pools after you unlock them. You just need to unlock them, then they stay unlocked forever.
However, yes you will need to go all the way back to being a villain to do the patron arcs.
Nelm, I apologize if this information is more basic than you need.
The reason that you see so many builds that use Mace Mastery's Scorpion Shield is that many players use Scorpion Shield's defense-based shield to build high-level defenses. Defense-based shields offer a way to avoid getting mezzed (such as being held or stunned) for builds that otherwise lack mezz protection (like most corruptors, defenders, controllers, and masterminds). Getting held or stunned can be the most frustrating aspect of playing a support character, and defenses can help prevent that from happening. Resistance-based shields, like Charged Armor, don't directly offer protection from mezzes.
This is because defense-based shields and resistance-based shields work differently. Defenses prevent you from getting hit in the first place. Resistances prevent you from being hurt as much when you do get hit. If you're concerned about getting mezzed, you want to avoid getting hit at all. If an enemy's attack contains a hold component, a resistance-based shield does not protect you from being held. A defense-based shield might keep you from being hit with the attack and therefore prevent you from getting held.
Most of the patron/epic power pools offer resistance-based shields. The exceptions are, IIRC, Mace Mastery, Ice Mastery, and Earth Mastery. The latter two aren't available to corruptors or defenders, unfortunately, so Mace Mastery is often the power pool of choice for those two archetypes.
For characters that have mezz protection (some support powersets like Sonic Resonance, Force Fields, and Traps offer mezz protection to the person using them), deciding between resistances and defenses can be less important.
If you typically team with folks who can provide mezz protection (or defenses) to you, then deciding between resistances and defenses might be less important also.
There are likely good discussions about defenses versus resistances, and what the softcap means, and so on, but I can't direct you at the moment.
So many of the builds I have found and wanted to use as a model have selected Web Envelope and > Scorpion shield. I was unable to select those because I took my DP/Kin to the blue side after Praetoria. Can I get access to those arcs I need to complete by being a Vigilante? Or do I need to become a full villain, respec while a villain and then switch back to blue side where all my friends play?
Instead of those two I choose Electric Fence and Charge Armor from Electricity Mastery. How do they compare to Scorpion Shield and Web Envelope?