Laundry reno - what can be DIY'd and what can't.

Looking to update our laundry - currently just the typical a free standing supertub and a washer & dryer sitting in the alcove of the garage, with some melamine racking shelves above it.

Wanting to scrap the shelves and supertub, put in a hardwood bench with an insert laundry tube with a sink mixer that has a pull out tap/hose, space underneath for the washer/dryer and box in under the sink for a cupboard. The selves above the bench.

Reading what you can legally DIY plumbing wise is a bit confusing (or more rightly confusing that it seems so restricted). From what I read it would seem like I have to have a plumber to fit the sink and tap? Is that correct or can these be done DIY - I know I would be competent enough do the work, but legally can I? Seems a bit excessive, but at the same time I can also see how you could screw it up and cause major (potentially life threatening) issues.

Also what would a plumbing give me regarding "paperwork" to sign off on their plumbing work? It shouldn't need a building consent so what would they typically provide, i.e. if you didn't ask for anything specifically from them.