I would first check the rotors and caps, since it's a very easy job, there is a detailed description in DIY section.
If you have a fuel pressure gauge(I bought mine for Cnd$55), a quick 10 seconds measurement can tell you if it's a fuel system problem or not, just my 2 cents.
My 400E cranks longer than other cars before it runs.
99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.