I wish to make an iOS application that includes a document library, log/journal, forums, possible randomized quotes ?and coaching tools?, and have built applications of that size in other contexts but this is my first iOS application.
Right now I'm working through http://www.raywenderlich.com/1797/how-to-create-a-simple-iphone-app-tutorial-part-1 , and I'd welcome comments on other tutorials, but I wanted to ask: does it work to work out the logical gears of an application before developing the graphic design? I would like to have somewhere between a Dirtylicious and Nature look, but my natural bent (no pun intended) is to get most the gears working and then defer most of the design work until after the gears. I expect they should not be completely separated, and there are cases where you apply the design and then realized that what the gears are doing only looked good on paper, but I wanted to do a sanity check on whether it makes to look up tutorials appropriate to a document library, a log/journal, forums, etc. and get them to work together first, and then skin it.
TIA,
It is recommended that you follow the MVC pattern, which strives for separation between layers.
http://developer.apple.com/library/ios/#documentation/general/conceptual/devpedia-cocoacore/MVC.html
Xcode helps you implementing that pattern.
I think you should try to put in "paper" everything you want to do, before doing any actual coding, check how many views you are gonna have, what you need, the flow between views, try to diagram everything, that will save you a lot of pain later. You don't have to be so specific about the GUI at this stage, you only need to know what kind of visuals you need in the views, (buttons, labels, etc...)
And yes, I think you're safe doing the Model first.