Really cold days, try three times 30 seconds glow plug warm ups
.. ignition on, wait 30 then off, then on right away 30s then off, then on right away 30s and start up....
Take no notice of the dash warning light for the glow plug, its not related to when it turns off the charge... Glow plugs have a designated charge time via ECU and relay even if your car has started up before they have finished pre-heat, they will still be heating until the timer has cut the current
You should hear a click from the engine bay when the relay has switch the heating proceedure off thus (30 seconds)
Don't use Ether or easystart, your engine will start to depend on it.
If you still have an issue:
Check the glow plugs by using a multimeter to see if they are getting the correct current and voltage, one usually fails first, very rare they all fail together.
If in doubt take them out but keep them connected and see if they all glow red at the same time period, one slow at heating up will cause a problem
Black smoke is normal, it's unburnt fuel that hasn't reached compression burn temperature just yet, pistons and rings need heat to seal up properly so compression is initially down a little until heat builds up... That's normal... Time to be concerned is when its doing it when hot and usually down to a blocked EGR or MAP sensor
Its not rocket science but some people try and make it sound like it
You'll be fine mate