Should a freewheeling (flyback) diode be used on the coil of a 2-coil latching relay?
It depends, if your worried about an overvoltage condition on the line, then yes you do need a diode. The relay will open and the magnetic field will cause an overvoltage on the lines connected to the coil. If you have other IC's connected to the power side I would strongly consider a flyback diode. If it's an automotive application a flyback diode would also be warranted because you don't know what else is on the 12V line. If it's a motor or resistive load I wouldn't worry about it too much. 

As far as the switch debouncing goes, it depends on your application again. The relay could follow the switch depending on the timing of switch 'bounce'. If the application is a 'dumb' load and it can handle being turned on and off for a 10's of microseconds (potentially) then you don't need to worry about debouncing. If it is a microprocessor or something with digital logic, then debounce the switch. If you have a high current load its probably a good idea to debounce the switch to be nice to the relay's contacts.