Recommended keys are listed in the Wiki under Hotkeys. I don't know much about the plug-in but the plug-in and keygrabber are two different routes to get control via a gamepad. Keygrabber will not alter or configure the plug-in. As far as jog+ and jog-, I'm not sure I understand what your wanting. Page up and page down are + and - jog for the z axis for example. Arrow up and down are for the Y and Arrow left and arrow right are for the x unless your hotkeys have been altered (config., Hotkeys) Press your tab key to open or close the MPG page and see what your slow jog % is set to. Just pressing a jog key will be slow jog. Holding down the shift key and pressing a jog key will be rapid jog. Rapid jog is as fast as your machine can go dictated by your settings in the motor tuning pages. Slow jog is a percentage of your rapid. This is a link to a thread on Keygrabber that may help with it if you choose to go that route.
http://www.machsupport.com/forum/index.php/topic,1391.0.html If you know programming you can alter the joystick plug-in to do most anything I would say.
Brett