A couple of years ago we had a similar discussion and went for a caravan, but at the heavier Jayco end. Love getting out and about so wish you well.
Fully self contained is an absolute must.
Don't overestimate the amount of time you can spend out independently. We have built-in fresh and grey tanks, and find that 4-5 days is the max we can stretch. Toilet cassettes are getting pretty honky after 4 days anyway, but we have 2 cassettes (17 litre each). To empty and replenish fresh and grey waters we need to move the caravan. UK caravans are to light to have built in tanks so they use the roll in/out variety, been there done that. Has the advantage that it is easy to replenish/empty onsite by just rolling containers to the facilities, but you will have no disposal points at most DOC and NZMCA sites. Disadvantage is that capacity is low. And those tanks outside freeze in winter, we had to bring them inside overnight.
A good NZ forum resource is https://www.nzmotorhome.co.nz/
Many years ago had a 13' Swift, but that will bear absolutely no comparison to today's caravans so can't comment.