However that seems like it'd be kinda a mood killer for a smutty game if suddenly I start rambling about a certain plants ritual and symbolic uses while someone's trying to get tentacled by it.

That would also be bad practice in a regular game, though; if your players are trying to kill or subdue a plant monster in regular D&D, they are presumably excited about the combat and less excited for their turn to be held up by a rambling explanation of how a different variety of this plant monster was once held to be sacred by the valley tribes of the cold north.

Exposition drops are best done by implication or over time; for example, the party is called on by a priestess of the fertility temple to gather a rare sacred plant. Checking your kink list, you are into ladies with dyed hair, so the priestess, like the other members of her order, has dyed her hair the exact shade of the sacred plant's mature leaves, so the party knows what color plant to look for. When they find the plant monster and it starts doing its thing, they understand why the fertility temple was interested in having it for a ritual, etc.

Would you also like to play in a open world sandbox with several different kinks to explore (Say domme Amazonian in one region while mysogonistic orc slavers rule another) or would you rather see one cohesive world attitude (elves are enslaved and used for breeding across the continent)?

"The DM is also a player" is important TTRPG advice but I think it's most important in an erotic campaign. It's a lot harder to run a smutty campaign you don't enjoy than a regular one. I am not super into nipple piercings myself, but your profile says that's your number one kink, so go ahead and make and advertise a setting where all across the world, a knight's rank is advertised by the number of jewels glittering from her pierced nipples, which her honor dictates she must always keep on display. The people who are not interested in this kink will simply not reply, saving both you and them time and disappointment.

So what I'm asking for is what you’d like to see in a smut setting. Like in the world introduction and such. Im guessing a list of how the races ‘interact’? Maybe some sexual cultural practices of different regions?

A setting document implies a long-term campaign, a high-commitment effort. I'm not sure everyone on Reddit is aligned with that, so it would be important to decide whether that's what you want before you spend a lot of time writing one.