1) There is currently no adjustment for DPI in ArtRage - it's been a much-requested feature that we're looking at adding to a future release
2) The native DPI of ArtRage is 72dpi to match monitor output.
3) 'ArtPen' is a control in the felt-tip (or marker) pen. Switching it on gives more opaque ink when you're using lighter colours.
4) The version of the manual is '2' - so long as it mentions layer blend modes, it's current for the latest version of ArtRage 2.2 When you upgraded ArtRage to version 2.2 you should have received the latest manual with the upgrade.
5) Adjust the 'pressure' radial in the settings panel for the airbrush to be lower. And you can make your working layer more transparent to add subtle effects as well.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"