How to Play Contagion and Essence Drain, Plus questions for GGG

After many hours of testing these are my findings. Still a lot of questions though.
Currently I am using: But will change up Essence Drain Support gems as I can get the right colored sockets.
3 link Essence Drain-Void Manipulation-Rapid Decay (due to socket colors available).
3 link Contagion-Controlled Destruction-Increased Area of Affect
4 link Wither-Spell Echo-Cast Speed-Increased Area of Affect

Killing Groups:
I found that it is best to cast "Contagion" first on a group and then lob a "Essence Drain" towards group.
1. You may not hit the mob you were aiming for but it would not matter which mob you hit as long as the "Contagion" hit it first).
2.Try not to hit the boss if possible as you want the fist one you hit to die fast and keep spreading the damage to any mob which is then close enough to the one that dies. (If you do hit boss first run and recast Essence drain towards group again)
3. Do not use "Whither" on groups unless it is a "Blue" group which is not dieing fast enough to spread to others. Or you get down to a single mob which you want to die faster.
By doing this every time a mob dies it spreads and spreads, and hopefully every mob that dies is near enough to the boss mob to restart the debuff on it.
4. If Contagion is killing white mobs before you are able to apply a Essence Drain, remove support gems which increase the damage of Contagion. You can still use, and I suggest using support gems like "Increased Area of Affect", "Increased Duration" and "Faster Casting" in that order (area is more important than duration, and then casting speed, more area hits mobs further away). If you have more than 4 sockets maybe throw in a "Culling Strike" or experment with other support gems to see what you like.
The reason for this is that you do not want to kill mobs with Contagion alone, before getting an essence drain on the group.
Killing an all white group is all good but when you have a boss or a white and blue group at the same time you want Essence Drain to kill them while Contagion is applied, so that the higher DPS debuff is the one hitting the blue or boss mobs.

Single target: (or 2-3 single high life mobs)
1. Best not to use Contagion at all. Just cast "Essence Drain" on it (or on each one) and run.
2. This is where "Wither" comes into action. As long as you are "Safe", spam it as many times as possible (as it is supposed to stack up to 20 times). I have not been able to confirm the stacking because there is no icons that come up to inform you how many stacks (of Wither) are applied. "Essence Drain" does have an icon, which has a number under it indicating how many mobs are currently affected by it.
Also, I am not sure you can get 20 stacks up before the DOT runs out, and you have to re-apply "Essence Drain" again.

Suggestion or request for GGG:
1. Please make icon for "Wither" indicating how many stacks are up on a single mob. If you use it on a group I am not sure how it would display.
2. Make "Wither" self stacking once applied. (% of damage for every x amount of time it is on mobs, I got my cast time for it down to 0.23 seconds) I am not sure how this could be done but I do know that I can not stand long enough to cast it so many times before the mob is on top of me again.
3. Make "Wither" an Aura somehow?
4. Look at DPS values when hovering over "Essence Drain", "Contagion", "Wither", or any other Chaos damaging skills. Currently, People should be looking inside details (below top line). The reason for this is that if you add "Spell Echo" or "Faster Casting" the top line will show (example:) 2000-dps, and down in the information area it will show 1400-dps. So basically they are showing non-correct data.

Questions:
1. Can you look into "Passive" nodes like "Amplify". (and any Jewels if they exist)
I added all 3 of the group at one time and the details DPS did increase but there is no indication that the "Increased Radius of Area Skills" attaches to any of the 3 Chaos spells discussed above.
However, if you use the "Increased Area Damage" gem it does place or increases the area in details (when hovering over skill).
2. Can you look at the "Passive group" "Corruption" also (and any like it). I did not see any increase in my DPS when I selected this entire node. I do not have the re-spec points to test out removing them and checking the details instead of the top line DPS when hovering over skill.
3. "Wither and Contagion" DPS (top line) goes away if there is no "Adds x-xx Damage to Spells".
4. Why would "Wither" have any DPS associated with it, if it is just supposed to amplify the Chaos damage from Contagion or Essence Drain? The DPS only shows in the top line and no where in the details section when hovering over it.
5. "Blasphemy" Have not found the right curse to link this to yet. Currently using "Poachers Mark" but it does not appear the Aura radius is anywhere near big enough, and/or once applied to mob wears off before being able to apply your other spells on them. Any Suggestions here on a better Curse to use? (GGG or Other players)

Well I did not get everything in but this is lengthy, and if you made it this far I thank you for taking the time to read it all. Please respond with questions, answers, suggestions.

Wouldn't temp chains also reduce the effective damage per second of the DoT effects since the enemy experiences everything slower?

Though it is logical TC would affect it in similar way as 'enemies burn faster' on Goddess Scorned. I'd personally do it but devs probably think it would complicate things too much.

Thank you to everyone who has provided information.