1.
AQ5 is easy with a typical 100%+ assault grid with random 100% support. Max SL if you dont wanna bother with super supports. You only need enough firepower to stun Andromalius within 5 turns (about 5.5m dmg, 6T if you have BP), and more importantly to let you get through the miniboss, which is imho the only hard part of AQ5. Or just play turtle and stack 100% dmg cut with Jeanne + one tank hime + Kaiser cut.
youtu.be/Fqcu-4YknbA
Note that I failed the run on purpose to show what happens if you messed up on miniboss mechanic xD
GO actually has less requirement in terms of raw power. Perfectly doable even if you run SR team provided you have a decent grid + advantage + know what you're doing. Less if you have a full SSR team or a healthy mix of SSRs and SRs.
vs Thunder GO
youtu.be/IOEyPDN4xpQ
vs Light GO
youtu.be/Eo7p2xYRPS4
Tower I will mention in response towards Slashey. All I can say is, do not take it lightly.
2.
Hard to answer. I don't really have a fixed team as I change my team according to what I need or feel like trying. If you ask what team I use for daily chores like Rag raids and GO, then it's Herc, Takeminakata, Mikael, SSArty + wild card (Tsukuyomi or Freyr or Shamash or Sol depending on fight).
3. Quite a few. Most involving the big 4 meta heroes + Mikael, SSArty, Tishtrya, Takeminataka, Tsukuyomi, Freyr or Vishnu + Sol or Eros if defense, cleansing or dispel is needed.
GO is ezpz with a average SL15~20 grid + elemental advantage.
Tower though, if you aiming for higher currency reward, nothing less than maxed SL grid + several +99 OR 2~3 FLB weapons (for extra skills) + close to max SL grid (no +99 needed). Thing is, you aren't going to be using your shiny SSR team for most of the floors because you need to save it for the final fight. You will be rotating through Rs, SRs, and probably your spare SSRs of a single element if you have any left. Not saying it's impossible to succeed with less, but I would not recommend it unless you have a thing for cutting it real close. Plus even if you meet all the hardware requirements
youtu.be/2U9r_Sv6tY8
nicovideo/watch/sm32850263
Simple mistakes can easily cost you your effort throughout the entire course of event.
The one's that I know of are mainly the hero ones plus Cthulhu, Satan's A frame, Ryuuou and Tyr.
There isn't really an official list but more a shared experience among players in active communities. In fact if you take a closer look at JP wiki comments you will find frequent complains about the accuracy of those few debuffs I mentioned. OTOH, notoriously accurate ones that I know of (and can confirm) are Amon U, Amaterasu (and her NY ver) and Samael.
Pardon me but I'm gonna have to address this post here because it's relevant to Light builds and I'm not about to let this misinformation overlooked. Just FYI Herc Weapon debuff is 25% and she can do it faster and better with her Burst Gain Rate up from Abi1 + 30 Burst Gauge from her Axe upgraded Abi3. Secondly, that 30 Burst Gauge I mentioned is exactly why she is meant to be used with PF. Saying that she's inferior to Vine's mere 10% is just, excuse my language but, ignorant.