This is a shirtwaist.
I would think that a regular blouse pattern should be sufficient. The reason why you don't want to get this done to the letter is because it would be difficult to wear and the shape would be a bit odd, unless you have the proper corset. With this being an early-Edwardian shirtwaist, you'll have to take a consideration at the shape of the female form at this time - the S-curve corset pushed women's breasts forward and their rears back. The front, however, has a bit of extra fabric, which is due to something called the 'pouter pigeon' look - it adds a bit more to the top half while emphasizing the smallness of the waist. Luckily, you can still do this.
Good luck to you.