There are many possible causes for loss of coolant:
Visible radiator hoses - do an inspection. Look for signs of rust deposition from dried radiator water.
There is a tiny section of radiator hose between the front engine thermostat housing and the water pump I think. It's a regular inch or so length of hose that is hard to see unless you know where to look.
Pinholes in the radiator - look for the signs of water leaking out under pressure.

As for hard starting - glow plugs, glow plug timer, wires. Lack of air flow - check filter for blockage.

Fuel delivery as stated.

Also as suggested, don't jump to conclusions that all is lost. Check the little stuff first and rule it out.

__________________
Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)