1. Is there a ban on donations from foreign interests to political parties?

207 Interpretation […]
(2) In this subpart and subparts 4 to 6 of this Part, unless the context otherwise
requires,— […]
New Zealand person means a person who is not an overseas person
overseas person means—
(a) an individual who—
(i) resides outside New Zealand; and
(ii) is not a New Zealand citizen or registered as an elector; or
(b) a body corporate incorporated outside New Zealand; or
(c) an unincorporated body that has its head office or principal place of
business outside New Zealand
Source: Art. 207(2), Electoral Act 1993, (amended 2020)

207K Overseas donation or contribution may not exceed $50 […]
(2A) If a party secretary receives from an overseas person a donation that either on
its own or when aggregated with all other donations made by or on behalf of
the same overseas person during the same year ending 31 December exceeds
$50, the party secretary must, within 20 working days of receipt of the donation,—
(a) return to the overseas person the total amount donated by the overseas
person, or its value, less $50; or
(b) if this is not possible, pay the total amount donated by the overseas person,
or its value, less $50 to the Electoral Commission.
(3) If a candidate or party secretary receives, from a donor who is not an overseas
person (as defined in subsection (1)), a donation funded from contributions that
includes any contribution exceeding $50 made by or on behalf of an overseas
person or any contributions made by or on behalf of the same overseas person
that when aggregated exceed $50, the candidate or party secretary must, within
20 working days after notification of that fact under section 207C,—
(a) give back to the donor the amount of the donation, or its value; or
(b) if this is not possible, pay the amount of the donation, or its value, to the
Electoral Commission.
Source: Art. 207K(2A-3), Electoral Act 1993, (amended 2020)

There is no ban, but there is a NZD 50 limit on such donations.