Are you using the latest version for OS X? The magic mouse and trackpad work fine on OS X with PixInsight version 1.8.4.1195. For the trackpad, the default application settings generally work well, but you may want to experiment changing pinch zoom sensitivity (Edit > Global Preferences > Miscellaneous Image Window Settings > Pinch zoom sensitivity).
If you are using an older version (e.g. 1.8.3, or build 1123), you should install the current 1.8.4.1195 version, where all of these problems have been fixed.