After having some time to work on my old 1981 240D, I finally bumped into the most frustrating outcome of all the hard work:
the car could not start at all, just like it had been before I started working on it. I have done some necessary work on the damned thing:

1) Change engine oil to Chevron Delo 400.
2) Change power steering fluid
3) Adjusted valves lashes (Intake = 0.1 mm, Exhaust = 0.3 mm)
4) Replaced spin-on main filter, inline pre-filter
5) Bleeded air out of the fuel lines using the primer pump
6) Fully charged my battery using a battery charger
7) Confirmed that all 4 glow plugs work as expected (red hot glow)

8) Cranked the engine in order to start it, but it simply could not start! :-(

My questions are:

1) Is the coil resistance of my starter has become too big, making it hard to rotate the crankshaft fast enough? I don't know how fast is fast, but the cranking seems to be OK to me.

2) I stupidly forgot to press the accelerator pedal to the floor while cranking (thought I did need to press the accelerator while cranking a diesel). I did let the glow plugs work for several cycles before trying to crank the engine. Does a good diesel car can just start easily without a need to press the accelerator while cranking?

3) The car will start if being push-started. Is this ONLY due to a weak starter?

4) I didn't know how the compression level in each cylinder is. Is it possible that my car could not start because of bad compression
levels?

5) Is that true that bad diesel fuel will make starting impossible?

6) Any other suggestions?

Please help a desperate soul. I'm tired of diesel cars now :-(

Eric