Jessica,
I used to publish on Smashwords and Amazon. Amazon was great when you could advertise Erotica on it, but now that you can't, not so much. It's very hard to publish and advertise on Smashwords. Smashwords doesn't have any in house advertising. Advertising for erotica is a hard find, and there are just some things you can't sell commercially in erotica. Incest, rape (as a main plot element), and under 18 are all no no's. I always made more from the distribution network than from Smashwords itself. They put you on a ton of book sales sites. I most often receive royalties from Black Puma through Smashwords. It isn't setting the world on fire, but it has purchased dresses, shoes, and some really nice wigs of late.
Smashwords was very good to Pops for years. But when he pulled down all the stories from his different pen-names he never got them back up for sale. Of course, Pops doesn't write erotica. I have my work edited though Writers Digest services and buy the proof reading service. It is a very good edit, cost $2.00 a page (double spaced, 12 pt, Times New Roman) I don't remember the minimum but I usually several short stories at one time and sent two to three hundred dollars worth at a time. They levels above that but the proof reading is a full edit. I paid for what they called the Edit level, and the same story done on the proof read level and found very few differences.
There are publishing houses that specialize in Erotica I think one of my authors uses one of them. I'll try to go through my old notes and see if I can't find you a publishing house that does erotic horror.
All the best luck
Millie