"The issue that lead to the car stalling, etc turned out to be a vacuum leak coming fron under the fuel distributor hence its disassembly and re-assembly"
If you mean the airpath to the idle control valve was leaking, this is what caused occasional stalling and other problems in our 2.3
"With the two items above in mind, I have the following questions:
1) What is a nice short test to find out if the fuel accumulator is bad? Is the cranking but no engine start X3 the best test?
2) Is the cold start valve the same as the starting valve, mentioned in the service CD, and is this the same as the fifth injector?"
I would think leaving the ignition on a moment before starting would get around a leakdown , whether from leaky injector check valves, bad accumulator, or other. Our car always starts more smoothly if I do this - but it always starts anyway if I don't. I doubt if this is your starting problem. Even when I have depressurized the system and bled the injector lines (then reconnected all), the engine starts after just a few cranks of the first attempt.
Since you have 6 ports with injectors, I could see the cold-start valve being called the 'seventh' injector, but not fifth. Maybe it's a term left over from when most engines were 4's? Anyway, pull the plug on it and see if anything changes.