EBook sales vary from genre to genre – but if you are writing erotica, and you are a new author, I would suggest you set your expectations at around 2-3 books a day.  According to a report in the Guardian, half of self-published authors make less than $500 a year off of book sales.  The average self-published author makes around $10,000 a year.  That means you have a group of authors making a good living, and a ton of authors making pocket change.  It might take eight books before you find your best seller – that is normal, do not beat yourself up if you are not the next E.L. James.  Be incredibly proud of your accomplishment and rejoice over every single sale.  Someone out there finds your book interesting enough to spend money to purchase it, and time to read it. Visit the KDP author forums – you will find that those authors rejoice over 2 sales a day – erotica blesses its authors more than other genres, you can expect a slightly higher average.  But, set your expectations low and hopefully you will be pleasantly surprised.  J

Good luck, and keep writing!!!!