Help in assessing the input mains circuit integrity
I need to be able to know how much energy/ voltage and the where bouts
of the circuit operates in a surge , fast transient and ESD situation

and

How do you calculate/simulate or choose the correct MOV model/value
for the above application to pass the test conditions mentioned above
?

You need to model the way in which the surges, bursts and ESD are applied to your live and neutral connections. There will be an interface circuit for all three and, these circuits should be locatable on-line. For instance, indirect lightning surge testing is available because I've researched it myself to uncover whether some TVS diodes (that I was planning on using for a particular job) were man-enough to withstand the surges.
So, do some digging and uncover those circuits - they won't be too tricky - you can easily model the waveforms with straight lines ramps of voltage; it doesn't need to be exact - reasonable approximations to the waveforms are good enough but, the important thing to model is the surge/burst/discharge source impedance because this tells you how much current is fed to the protection device when it is protecting.
In my surge example above, I had to deal with surge voltages at a peak of 4,000 volts sourced through a 2 Ω series resistor. In other words, the peak current could be up to 2,000 amps. So, I modelled it and simulated the surge protection circuit and determined how much peak energy I might subject my TVS to. Then I looked at the data sheet for the TVS and worked out whether I had a comfortable enough margin.

if the input protection fails then I have not backup plan

Your only back-up plan is diligence - have you got a comfortable enough margin. I mean; if you don't simulate and get a feel for things then you have no idea whether the protection you fit is anything like suitable so, do the right thing and model each threat in terms of voltage waveform and output impedance and model each protection device to see that you don't exceed the peak energy handling in the data sheet (and add a comfort margin of 1.5).

Will the current Input stage of the Power Supply survive the Tests
mentioned above ? ​

You can be sure if your modelling and simulation suggest not, then you need to improve things. But, of course, the real test is the lab test. My surge test (EN 61000-4-5) was a pass if that gives you any confidence in things but, I probably spent two solid weeks with a simulator.