look in the system prefs http://goo.gl/PvSTK

negative linespacing? the SpaceCenter only gives some basic layout options if you want to test your font with more depth I would recommend to try test install and setup a template in text setting app. In the waterfall mode only the first line is editable :)

yes, that is producing the same result the space after a /<glyphName> is mainly because you can use both non-glyphName and /<glyphNames> as input: Su/cool_p er p (if you have a glyph called cool_p) Copy paste glyph in the input field will try to convert them to unicode characters for display in the input field, that is way the extra space is added. You could also drag and drop glyph on the input fields.

There is a scripting possibility to access, change and manage the input string for the space center see http://doc.robofont.com/documentation/scripting/api/mojo/mojo-ui/ (CurrentSpaceCenter) If you store user defaults through the app its will be fine. no worries :)