Lamphater,
The Q&A forum might work better to get answers to your questions.
As far as your first question, in most of space, the pressure would be essentially 0 psi. Depending on exactly where you were (for example, how close to a planet with an atmosphere, on in the solar wind from the sun) and how precise your gauge was, you might get readings of 10
-11 to 10
-20 Pascal.
One reference