is there a place where I can find common "shortcut patterns"? what't the common usage of ctrl+click, alt+click, shift+click? I need to add some advanced shortcuts/gestures and I don't want to use one that usually is used for something else

This will depend on the domain and platform. For instance, on Mac, it's common that command-click is used for adding single items to a selection, and shift-click is used for adding ranges of items. On Mac, control-click is almost always used to open a contextual menu (same as right-click). Option-click is far more situation dependent. 2d graphics applications have their own standard conventions. For instance, it's common that holding spacebar and dragging is how you pan the view. For 3d graphics — and games for that matter — it tends to be unique to each.