> 4. As long as there’s a neutral line, i think any common mode should be rejected, in which case this should be fine?

The (grounded) neutral conductor actually completes the circuit, a wye/star transformer has a grounded neutral and the primary and secondary neutral terminals are bonded. The return path is ground and all of the transformers are linked together via the grounded neutral.

Apparently this can be mitigated by wiring a capacitor into the grounded neutral path of a wye transformer.

I’m not an EE, just an electrical PM who knows enough to be dangerous :)