I'll post about this with a bit more depth with numbers from another month or two.
So far here's what I have:
I put up Saltwater Witch, Seaborn, and Sea Throne on Amazon.com, B&N (Nook), Apple iBooks, and Smashwords around the middle of March. Here we are twelve days into May—so roughly 7-8 weeks of sales, and I've sold just under 600 books.
Saltwater Witch has been hovering in and out of the Top 100 of "Bestsellers in Books > Fantasy > Magic & Wizards" at Amazon.com, which is pretty cool. All three books have been in the Top 100 in "Kindle Store > Books > Fiction > Fantasy > Contemporary" on Amazon.co.uk, getting down into the 40's. So not too bad.
Okay, all three books--Saltwater Witch, Seaborn, and Sea Throne--are now available under one "cover"--along with some all new transitional material from Michael Henderson, an extra story, and dramatis personae. $7.99 on the Kindle.