Palmerston North is boring. Whanganui has improved over the years but Palmy has gone backwards.
You'll need a car (ideally one each). It's quite spread out but mostly flat. Whenever I'm there I find myself going out in the car multiple times a day.
Renting or buying? There's a real shortage of rentals in NZ. House prices have gone up a lot. I wouldn't accept any place that doesn't have a proper heat pump. Central heating is not a thing.
Foxton Beach is a very average beach. I would not live there. If you live in any of the little towns surrounding Palmy you will find yourself always in the car driving to Palmy. It's about a 45 minute drive.
Weather isn't great. We were there for 5 weeks Dec to Jan and only had one week of sunshine. It's windy but great for drying washing.
Palmy is not in a great location. 2-3 hours drive to Hawkes Bay, Taupo, slightly less to Wellington. A long way to Coromandel, Auckland, Rotorua. Driving to and from Whanganui was quite taxing (approx 1 hour).
It's easy living - can take the kids down the river very easily, playground at The Esplanade (Park) is really good and my kids love the miniature railway, it has most shops you would want. Lido swimming pool has improved, nice cafes for brunch etc. Schools mostly good.
Cost of food (supermarket and cafes, restaurants) was comparable to London. Food is fresh. Portions huge.
I could go on and on. What questions do you have?