7.3's use a glow plug system that is based on resistance (ohms). Cold glow plugs should be below 1 ohm, so all 8 should show about 8 ohms to the glow plug controller. When you turn the key, the glow plug controller sends out current to the glow plugs. As they get hotter, there ohms go up. So when the glow plug controller see's that the ohm rating went from 8ohms with cold glow plugs, to x ohms (probably like 2000ohms or something) when they are hot, it shuts off current as the glow plugs are hot enough to fire up the truck.
Sounds good right?
Well if a glow plug burns out, it will have a REALLY high ohm reading. So all the other plugs may be good, but one plug will read a high ohm reading. So instead of all 8 plugs cold being 8 ohms, it could read 500ohms. You turn the key, and the glow plug controller will only stay on until it reads X ohms which will happen faster. But staying on for a shorter time means that the glow plugs dont get as hot, which means hard starts.
Clicking right away means either bag plugs, or a bad controller. Take each glow plug ohm reading and if they all check out less that 1 ohm cold, its the glow plug controller.
White smoke is unburnt (really unburnt, like cold unburnt instead of hot unburnt which is black) fuel. Its white cause its not even hot enough to semi-burn the fuel to make black smoke.