Okay, let's break this down and address your points. Your assessment seems largely correct, but let's refine a few areas for clarity and best practice.

Assumptions



SE Rated Transfer Switch

This is crucial. A service entrance rated transfer switch can handle bonding neutral and ground within it. If it is not SE rated, then the neutral cannot be bonded in the transfer switch.

All wiring is copper. "Building Steel" is indeed structural steel integral to the building.Here's a breakdown and adjustments based on your description


GEC (Grounding Electrode Conductor)



#6 Bare Solid

Seems Correct. For a 400A service, a #6 copper GEC is usually sufficient for connecting to ground rods (250.66 and Table 250.66).

Meter Can to Two Ground Rods

Correct. Ground rods should be at least 8 feet long and driven at least 8 feet apart.

Bonding Strap in Meter Can

Correct. The factory-provided bonding strap from the can to the neutral lug in the meter can is standard practice.2.

Meter Can to Transfer Switch



Parallel 3/0 for Phase Conductors and Neutral

Potentially problematic and requires verification. For a 400A service, you typically need conductors rated for at least 400A, accounting for ampacity correction and adjustment factors. While two parallel 3/0 copper conductors might be sufficient depending on insulation type and environmental conditions, you need to

verify the ampacity based on 310.15 and relevant tables, and any derating factors (temperature, number of conductors in a raceway). This is critical. 400A / 2 = 200A each so each parallel run needs to be rated for 200A after derating. 3/0 copper is only rated for 200A in the 75 degree column. You'll need to adjust to the 90 degree column and ensure all terminations are rated to accept 90 degree conductor. Important Considerations



Parallel Runs

All parallel conductors must be the same length, material, and insulation type. They must also be terminated in the same manner (same type of lug, torqued to the same value). (310.10(H))

Neutral Sizing

Is your load largely nonlinear? Consider that the neutral must be sized for the load it carries. A demand factor might allow you to reduce the neutral size if you do not anticipate excessive harmonics.

Raceway Fill

Ensure your conduit fill is within the code limits (Chapter 9 of the NEC).3.

Bonding in Transfer Switch



Neutrals and Equipment Grounding Conductors are Bonded in Transfer Switch (first means of disconnect)

Correct, assuming the transfer switch is SE rated. This is a service disconnect. This is critical to ensure the transfer switch is rated for use as service equipment. If it's not SE-rated, you cannot bond neutral and ground here.4.

Transfer Switch to Building Steel



1/0 Copper to Bond Building Steel

Generally Correct, but dependent on building steel size. 250.104(A)(1) requires bonding the building steel to the grounding electrode system. Table 250.66 would typically require a 1/0 copper conductor for a 400A service to bond to the building steel if the building has a water pipe that is used as an electrode. Since you are bonding directly to the building steel, consult 250.66(A) to ensure that the 1/0 copper is adequate. Also, ensure the connection to the building steel is made with approved methods (exothermic weld, listed lugs, etc.).
5.

Transfer Switch to 200A Sub-Panels



#3 EGC

Correct. Table 250.122 requires a #3 copper EGC for overcurrent devices rated at 400A. Since the 400A breaker in the transfer switch protects the feeders to the sub-panels, the #3 EGC is the appropriate size.

PVC Raceway

Acceptable. Ensure the PVC raceway is adequately sized to accommodate the conductors and the EGC.

Insulated Neutral to Subpanels

Correct. The neutral at the subpanels should be insulated and isolated from the panel enclosure. The ground and neutral should

NOT be bonded in the subpanels.

Important Considerations & Clarifications



Grounding Electrode System

Make sure your grounding electrode system is complete. Ground rods are a good start, but consider whether a metal water pipe or building steel is available and suitable as additional electrodes. If a metal water pipe enters the building, it must be used as a grounding electrode (250.52(A)(1)).

Separation of Neutral and Ground

Absolutely critical. The neutral and ground must be kept separate at the sub-panels. Only the service disconnect (the transfer switch in this case, assuming it's SE rated) should have the neutral and ground bonded.

Torque

All terminations must be torqued to the manufacturer's specifications. Use a calibrated torque wrench.

Labeling

Clearly label all equipment (meter can, transfer switch, sub-panels) and raceways to identify their function and source.

Ground Rod Spacing

You said you're going into two ground rods. You can run a single GEC to the first rod and then a jumper to the second rod, or you can run a GEC to each rod. In either case, the rods must be spaced at least 6 feet apart to reduce the possibility of overlapping soil resistance areas.

NEC 250.4(A)(5)

Ensures that effective ground-fault current paths are permanent and continuous.

Inspectors Local to Your Area

Always confirm the local AHJ has any specific requirements for this type of installation.

In summary: Your initial assessment is mostly on the right track. Double-check the ampacity of your service entrance conductors (3/0 copper) to the transfer switch.* Ensure they are adequately sized after derating for the conditions they will be subjected to. Ensure your transfer switch is service entrance rated! Ensure you have the neutral and ground separated at the subpanels. Properly torque all connections. Flag for review