1) I'd say its pretty unusual but not from any personal experience or knowledge
2)
https://law.justia.com/codes/new-york/2021/eln/article-17/17-152/
seems pretty vague, but I don't make the laws (seems to me that its probably not used near enough)
I'm not a tax expert but my guess is that if trump had paid it out himself- it would have been deductible.
Since it was a reimbursement - it was more a loan repayment and not? not sure
the campaign finance law had to do with the limit. 130k was above the limit he could do, but I don't have the exact law at hand
followup answers
1) they were in the indictment so its not like they were a mystery
2) the legal expert was going to testify about his interpretation of the law and nothing else. The judge correctly declared that is the duty of the judge