I have a MB E300 TDT s210, and I wonder if the injectors need replacement?

• Takes a "second" longer to start when cranking, than normal
• Is running pretty even, but with small "coughs" when cold and on idle
• Has white smoke coming out
• Has a lot white smoke coming out when driving it when it is cold
• After the engine is warm, it is not smoking much
• Has a harder sound than I believe it should have

I know 1 glow plug is defect, but still I don't believe that is sooo important on a 6-cyl engine?

Engine has run about 280000 km.

Is there an easy way for me to test this?

I've seen videos on Youtube where people just replaces the nozzles. Is that easy and straight forward (as it looks)?

What costs new injectors, and if only changing the nozzles, what is the price for them? What make of nozzles/ injectors should I choose?

EDIT: I suddenly remembered I posted here earlier. Read it up now. So then I know how to find a bad injector. However my questions above are still valid :-)