Quoting "THE NEXT major defence project on the books after the C-130J Hercules and the Boeing P-8A Poseidons are replacements for the RNZN’s two Anzac Class frigates Te Mana and Te Kaha. While these are due to remain in service until late in the next decade, planning is under way."

I would like to point that after C-130J Hercules and the Boeing P-8A the planning process for the Enhanced sealift LPD/LHA starts as well as naval helicopters, and Canterbury replacement and frigates. There is also a lot of smaller projects in-between them as well, including but not limited to; the LOV replacement and NZLAV upgrade or replacement.

Quoting "In a sense the RNZN’s role is similar to that of the US Coastguard."

While I understand (I think) what they mean and trying to say, however, the Royal New Zealand Navy is much more than a coast guard. Coast Guard protect borders from illegal entry to the country perform Search & Rescue duties and in the US case drug control etc... but in the RNZN case fishery patrols and HADR. So from this yes similar and most coast guards are limited in armament... so basically this equal to our patrol squadron, the OPV's and IPV's.

However, the Royal New Zealand Navy also help protect various shipping lanes, anywhere in the world, pirate patrols anywhere in the world, the can adapt into any allied fleet and for general fleet duties anti-air and air-submarine and anti-ship and electronic warfare... They can defend themself from various threats, fro sea, land and air... and this is just the frigates. The RNZN also now can inject a small force, supply fuel and dry goods to any other allied navy vessel. Then new DHV and it's abilities to deep-sea diving anti-mine warfare, recovery missions
and when the SOPV this then changes again as we add in that ability, now stretching if we do get the LPD or LHD then this changes yet again, and the frigates then have escort duties of our own high-value target (HVT) of our own vessels and equipment.