I would be grateful for information about any legal requirements that must be met with respect to the period of time that a trust must retain any documents, such as minutes of meetings, financial records, correspondence, etc

“The formal records of a trust (agendas and minutes and formal reports to the trustees etc) must be kept for the lifetime of the trust, and financial records must be kept for 7 years per IRD requirements -though many trusts archive these also.  As I understand it, correspondence and minor papers can be judiciously weeded after a suitable period.
I have no idea who checks these things. My guess it that they only get checked if there is a problem so on this basis, many trusts keep everything!”

I am afraid we cannot point you to a law or regulation, that’s a job for the lawyers but we got this advice from a lawyer a little while ago and believe it is sound.