Hi,
1) it depends on what surge definitions your customer relates. If he relates to ISO7637-2 and your design fulfills the application note requirements (trace width, loop impedance...) then it should be O.K.
2) You need to look for "clamp voltage", not breakdown voltage. Clamp voltage is much higher.
3) Generally ESD and surge is different. Surge usually is for power supply ESD mainly at signal lines. ESD is way less energy thus maybe even your power supply capacitor may be sufficient. But ESD may be faster (in dV/dt as well as decay time) with higher voltage but also higher source impedance.
4) This is the classical ESD case.
Is the TVS
* fast enough and
* low capacitance
* high impedance
* and low clamp voltage enough
... not to modify your PWM signals, but protect the devices?
5) Which path? Which voltage?
A series resistor in my eyes is no good idea. Look for informations why they installed the resistor.
6) If you install it after the filter, then C3 will not be protected and L1 need to widthstand the surge current and voltage....but due to increased loop impedance the protection level will be higher.
7) it depends on the input signals and how sensitive your load is.
I recommend to
* ask the customer for clear definitions
* go through some application note regarding surge and ESD, maybe reference designs.
* look for PCB layout examples. A lot depends on correct current paths
Every related semiconductor manufacturer provides a lot of informations, maybe even videos.
Klaus