I'm going to make this really easy. There is no official reading order. ESTO Universe stories - so far - are all stand alone. Two short stories, one novella, and three novels.
If you'd like to read them in Universe chronological order:
You'll find mentions of characters from other stories sometimes and By Imperial Decree has two minor character appearances from an earlier story, but you don't need to have read the others to know what's happening in your current read.
The latest addition is, of course, By Imperial Decree - out now in ebook and paperback :)
Mischief Corner Books
Angel writes (mostly) Science Fiction and Fantasy centered around queer heroes. Currently living part time in the hectic sprawl of northern Delaware and full time inside her head, she has one husband, one son, two cats, a love of all things beautiful and a terrible addiction to the consumption of both knowledge and chocolate.