Developing for all four iPhone resolutions - how do you go about it?

Question

With iPhone 6 out, developing for both iPhone 4, 5, 6 and 6 plus is a must. I'm pretty new to considering adaptive interfaces / content when developing apps, so I'm looking for strategies on how to approach it.
My current case example is a graphic novel-type app. The development process is going to be short, so I'm looking to make an app that just displays in fullscreen on all phones, not necessarily taking advantage of the higher pixel densities. A lot of the content is bitmap pages that need to take up the full screen on all resolutions.
So what are your general strategies for going about this? As I see it, the first issue is the two different aspect ratios. The iPhone 4 is 3:2 whereas all the others are 16:9, so my idea is to first detect if the ratio is 3:2 or not, and make the app either adapt to iPhone 4 or iPhone 5 depending on the result. Apple's automatic scaling of older apps should then take care of scaling up to iPhone 6 and 6+. Correct?
Secondly, what is the next step? Do I save all the bitmap pages of my graphic novel in a 640x960 version (iPhone 4) and a 640x1136 version (iPhone 5) separately, then load the right one at runtime depending on the aspect ratio detected?
Thirdly, if I work in Flash Pro with a 960x640 canvas size, do I then load the correct bitmap version and place it in the top left corner of the canvas because it will then extend to all the edges of the screen - or do I 'center' the iPhone 5 version outside the canvas to make it fit? (Meaning do I place the content at x = 0 for the iPhone 5 version, or at x = - ((1136 - 960) / 2) ?
I hope these questions make sense, especially the last one, and would like to hear how you would approach a project with a short deadline which just needs to run fullscreen on all iPhones.

Answer 1

Do you have different versions of the graphic novel pages, or is there just one version of the page? If there is one version, can you crop into the page without losing anything important?
I would guess that there is one version, and that cropping into the page will lose something important. If that's the case, here's how I would handle it:
Make a stage that is 14:9. The size doesn't matter, but 1400x900 could be a good starting point.
Put down a background texture that fits well with the look of the other images. Make that fill the 1400x900 stage.
Place your page graphics so that they are within the center 1200x788 area of the stage.
Set the stage scalemode to "noBorder".
You now have a layout that will work on all devices, as narrow as iPad, and as wide as iPhone 5. All without any code. On the widest devices you'll see a bit of your background pattern to the left and right of the page graphic. On the narrowest devices you'll see a bit of background pattern above and below the page graphic. But you won't lose sight of anything important.