Don't know dielectric breakdown of the bobbin plastic, PLA plastic. Not sure that's important though.
I can't stress enough the importance of matching the coils to the WC, both for reactance and impedance. Ronnie says the primary needs to be 10ohm. I haven't figured out why yet, but looking at your 18 turn 14 gauge wire, I know that will be so little resistance that it doesn't come close. And Ronnie just reminded us recently that the impedance ratio on Stan's coils was 1:10. Not that it has to be that, but it give an idea of Stan's setup since we know the resistance of his coils and therefore also know the resistance of his WC.
Gotta piece all these things together.