I would start with one about 1mm. thick.
And sharpen the face to 45 or 50 degrees, depending on the hardness of what you are cutting.
Create a lift/clearance/belly of 15 degrees on the bottom and both sides extending from the point to the back of the graver.
You can switch to a thicker onglette or even a round graver and re-cut if you find you want a wider line.
As I don't know where you are located I can't recommend a brand of tools.
I'm located in California too. May I suggest you add your general location (such as California)
to your bio. It is helpful to giving you general advise on tool suppliers etc.
For you project you might consider starting out with an Onglette size #1.#022-626 from GRS if you don't have one in the correct or close size.