Given you have 10 days and given the uncertain weather
in NZ, I think getting to Parengarenga is optimistic. We have never been to Parengarenga but have heard it is very shallow with large tides, and not recommended. Given your time frame, I'd recommend Auckland
, Kawau Island, Whangarei Heads or Tutukaka, Whangamumu Harbour, Bay of Islands and Whangaroa Harbour (this is spectacular, don't miss it). Even then it will be a fast trip. If you have extra time, I'd spend it in the Bay of Islands, Mokohinau and Cavalli Islands, and Great Barrier Island, all worth a visit.