You can use the cap or not– we usually do not, but it can sometimes be helpful to have additional weight.
We are working on an expanded version of Hershey Text, which is more adapted to longer blocks of text. For the most part, it’s usually better to use a regular (but thin) font. A wider nib (e.g., Lamy M) helps to avoid double-line issues.
Sadly, the cancel button in Inkscape does not work whatsoever (in any context– not just in AxiDraw). I’ve urged the development team to simply remove the button.
So long as “auto-rotate when printing” is selected, a document in portrait orientation (taller than wide) will be rotated automatically when you print it– please see the user guide for more detail about how to set up letters to print in the correct orietnation.