+ how can I display a grid to measure/guide my largely geometrical shape drawing?
If you have one, can download one, scan one, or draw one,
then use layers in Artrage.
If it is a png file it will allow you to see threw it.
Make several layers and put it on the top.
You can always delete it.
As to your other questions experiment a few times with the DPI setting and the size.
If you try two sizes, and measure how much they changed you should be able to calculate how much more you need to resize to get it to the size you want. Artrage basically uses a 4/3 ratio output format.
Artrage size does set to mm. 25.05 w = 32.10 h
While in rescale painting, highlight the height or width, and type in a size then click on the opposite setting width or height and artrage will find it for you.
I hope that helps.
If something I said is not clear feel free to sent me a private message and I will see it sooner than I would a general message here. I don't have a lot of answers but I will share any I do have. Some might even be right!