Making a mockup (preview screens) helps to put all your thoughts together. Your future developer will appreciate that. Paper&pencil is good, mockups by Balsamiq/mockupbird/etc allows to add some interaction.
Mockups will allow you to realise what exactly has to happen between the screens. Maybe you'll want more functionality after that, maybe you'll see that parts of it are not necessary.
I saw a webapp targeted for mobile apps content delivery on HN some time ago. Google should find it. It may be faster/cheaper to build a custom solution for simple delivery. But extending it may cost a lot and reusing out-of-box solution may be cheaper in the long run. I'm not familiar with NewsStand API so I can't comment more in this front.
Mockups will allow you to realise what exactly has to happen between the screens. Maybe you'll want more functionality after that, maybe you'll see that parts of it are not necessary.
I saw a webapp targeted for mobile apps content delivery on HN some time ago. Google should find it. It may be faster/cheaper to build a custom solution for simple delivery. But extending it may cost a lot and reusing out-of-box solution may be cheaper in the long run. I'm not familiar with NewsStand API so I can't comment more in this front.