(1) How is the system supposed to tell the difference between a mouse click and a mouse drag? [One way would be to assume it is a click but if the mouse is still down after some period of time--half a second? less?--then it converts to a drag. But then the person who wants to drag will feel a hesitation before the drag starts. Another way would be to make it modal: That is, it depends on which TAB is currently active.]
(2) What is the purpose of double click? Why were you worried about implementing it?
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.