Speaking about ailments and poison for a Viper Strike build

Hi everyone,

(Oh there's nobody here, like if there were only shadows... oh wait...).

I'm trying to figure out some details concerning the poison mechanic.
(I passed a lot of time on the PoE Fandom to read the characteristics of what I have in my hands, and find a build that would be cool to play).
Recently I discovered with my Ranger Void Manipulation Support. I soon figured that my Shadow specialized in poison would be the best char to use this.
After that I found a Poison Support in a box. I thought to replace the Lesser Poison my Shadow had by this new gem. After this I found a Deadly Ailment Support gem in another box (god dudes, there's a lot of boxes out there).
I saw my DPS lower by replacing Lesser Poison by Poison, and now I see DPS lower by replacing Void Manipulation by Deadly Ailments.

My 1st question is : Considering Viper Strike as my boss config, I want to poison them with it, -- [and dash away to reapply poisoning every ~4 seconds and let traps help the DoT down the bosses (I do that in other H&S and it works very well, let's see what it does in PoE)] -- so, is it better to support this Viper Strike by either Poison and Void Manipulation, or Poison and Deadly Ailments, or even Void M and Deadly Ailments ?
(I have the gems in claws, I may need to change to another piece of equipment to have 3 support gems).

My 2nd question is : What's the exact difference between Supported Skills deal "X% more damage with poison" and "X% more chaos damage" ?
Is it like Chaos is on hit AND over time or just on hit, and Poison is just the ailment "poisoned" ?
In this case it would mean that it is normal that Poisson Support lower DPS when replacing Lesser Poison Support, but it would give me what I want : more DoT on the bosses, right ?

If it is the 1st case (chaos = on hit + over time), I assume that the answer to my 1st question Void + Deadly Ailments, and if it is the 2nd case (chaos = only on hit), I guess Poison + Deadly Ailments is the way to go.

Kind of a 3rd question : In my case, is it better to take the chaos damage and chaos over time multiplier nodes, or just the chaos damage ones ? I guess it's linked to the 2nd question. But currently I just take everything that speaks of claws damage, chaos damage and chaos over time multiplier. I might have understood the mechanics the wrong way.

I also have Bane with Despair to lower the chaos res and do an additional DoT to help me. Crowds are smelted by this, but bosses would be more difficult to down, so the help of more chaos/poison DoT is welcome. I assume that I would have to take some % spell damage, as Bane take spell damage to improve the chaos over time effect. Would this be a mistake or a good choice ?

So as usual I thank eveyone who can answer this partially or entirely, in advance, it has been a quite long and complicated text. I'm still reading things on the internet, and switched tabs while writing, so my text may be confused, just tell me if I wrote something weird, be it grammar or game related.