The damage doesn't matter at all for applying the status, only your status chance applies. Although, the amount of damage you have does matter for the damage of the ailments. You can only apply 1 stack of 1 ailment at a time at base, but you can get a passive that allows you to apply 2 different ailments, apply 2 of the same ailment, and so on. Stun (from physical damage) and freeze (from ice damage) don't stack.

The amount of ailments you can stack on an enemy depend on how many damage types you have and the ailment stacks you have. I saw in a build somewhere that you can get about 30 stacks of an ailment, but since you can have multiple ailments, that number obviously goes up. Unless you have a lot of attack speed and ailment chance, though, it doesn't seem worth it to go with more than 2 damaging ailments.

It's not a matter of how much exactly but what are your highest dmg types of said ailment across all gear and gems.
You just need to be able to do 1 points of dmg for the type of ailment you want to inflict. So the highest dmg type you do will take priority in the chance to apply it first. You can also look on the skill itself when you hover over or click and it'll show which ailment has priority (or which two if you take the passive in Cabalist tree).

Some skills also allow you to modify the base dmg type which will change the ailment kind you apply on the enemy. If most of your dmg type is toxic then poison will be the priority ailment. If you socket gems that have "adds x-y 'kind' of dmg" to attacks or spells and/or have gear that says the same then the type of ailment will change.

I see thank you for the input. Do you guys know how the passive Immortal Offering works? Apparently I have stun, poison, bleed, burn, shock, freeze, stasis weakness and curse, all at around 17% chance to cause ailment, yet I only ever see stacks for bleed, weakness, and stasis from the passive itself.

The damage doesn't matter. If your items have damage to attack from different elements you can literally equip them in a different order to change which ailments you are applying. For ailment build the only things that matter is %chance for ailments, % chance for specific ailments, %damage, %ailment damage and %specific ailment damage. That said you can also spec for crit and make ailments crit with one passive. Some skills can also apply random ailments. In that case it's a good idea to take the passive which gives you a damage boost per ailment type up to 5 stacks. Sometimes you will proc 6+ ailment types, 5 stacks per ailment leading to some crazy damage boosts.

Stun and freeze don't get reflected. As for the rest, I don't know.

The dmg from your attack and spell determine what ailments can be applied. If a spell does aether dmg it applies stasis, If you want a second ailment applied you need the according node of the skilltree. If you specc into this node your seceond highest dmg will be applied and the ailment chance on each dmg will determine if an ailment is applied.
Things get tricky if you want to apply 4 different ailments but an explanation for this will take to long ^^.

Not true.

Each spell has it's own damage type therefore it applies that ailment no matter what.

Some skills can generate random damage types meaning you can apply a bunch of different ailment types by using a single skill. This is specifically visible if you will pick Immortal Offering which gives you damage buffs depending on applied ailments. You will then see little icons in the left bottom corner for all ailment types you have applied. I usually have 6+ while using Gunslinger with the random element perk.

Grievous Afflictions node makes it possible to apply 2 ailment types instead of 1 with hits.

You can inflict poison and bleed with basic attacks and then still inflict burning with fire spells for example.

The ailment types you are applying with basic attacks are displayed in the character window and can be changed by simply equipping your gear in different order if you have items with +x damage to attacks or spells. They are not determined based on the damage.

The base element of a skill is not applied "no matter what", it's always just based on which damage type is highest; you can stack up Shadow spell damage for example and make it higher than the base Aether damage of Annihilation and the skill will inflict Cursed instead of Stasis.

i have the same problem. did you find out how to see the other stacks on screen

FFS..... i just type a fucking wall of text hit "Send Reply" and then "you have to confirm you mail".... Since im lazy and dont want type all again only the short version, how you apply them you have to get it by your own.:
only 7 Ailments matter:

Bleed
Poison
Burn
Shock
Weakness
Stasis
Cursed
​
​
Atm lvl 73 running easy lvl 115+. Not so OP as my friend who had a bleeding edge pre nerf build but it is still fine the Ailments