Wellington will be a great place to open a coffee shop - just be aware that there are LOTS of them there. So whatever you do, you need to be that extra bit special by a) making sure your coffee ROCKS and b) making sure the food you sell is top notch. There are too many places here that have *** cakes, rock hard muffins and terrible soggy sandwiches and people very quickly end up avoiding these places.
I'd find a good, local supplier or even better yet, bake some things fresh on your premises. Hiring a good chef and having good value, tasty menus offering seasonal ingredients seems to be a winner (at least with me and many people I know!

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Good luck! When you do open that place, be sure to let us know and I'll be happy to come and check you out when you're in Wellington.

Cheers
Susan