Can an IMC rating holder fly at night without a NQ?
No, the IMCR and the NR/NQ are separate.
Can I fly at night with my FAA ticket, bearing in mind I also hold an IMCr but no NQ and also an FAA IR?
I assume you mean in a G-reg. Your FAA PPL/IR gives you worldwide VFR privileges in that, plus IFR privileges OCAS. Your FAA PPL includes night privileges but the FARs require an IR for IFR, which you have, so the answer must be an unqualified YES if OCAS, and a qualified YES (which takes us back to that other chestnut) if in Class D.
I can't imagine any context in which having an IMCR would allow you to fly at night but not having it would not.
The night rating course covers how to navigate in the dark, a little brief but does.
What does it teach? It was dead reckoning when i was doing it. One gets no extra instrument nav during the NQ.
The tiny bit of time under the hood during PPL training should be enough to tell you how to read the AI to see if you are plumeting to death
Which is going to be really useful
