From what you describe - I lean heavily towards a glow plug circuit problem. If the car is hard starting when cold but starts right up after sitting for an hour or so - It most likely is glow plug related. Since the plugs are new - I would get a cheap multimeter and set it to the 20 volt range. First thing in the morning, don't start the car - hold the black lead of the multimeter to the engine block and put the red wire onto one of the glowplugs - have someone turn the ignition on - if you don't have 12 volts at the glowplug - check your fuse and relay - I am almost certain you have no power to the glowplugs resulting in the hard starting. If your compression was bad - it would crank and crank to start - no matter if the engine was hot or cold - less cranking time when the engine was hot. If it starts up no problem when the engine is warm - - definately check for voltage to glowplugs - I would say 80% - that is your problem. The billowing smoke from the exhaust when it does fire is the unburnt diesel from the cylinders not being hot enough yet for complete combustion - translate - no glowplug activity. Let me know
Maurice