Building iphone application, Design Resolution

I have a couple of quick questions for building an iPhone unity game.

My questions are in regards mostly to the iPhone resolution when building a game. As i believe an iPhones resolution to be 320w * 480h.

My first question is am I supposed to set this in Player Settings when trying to build the game. Because its pretty important to my game that I know the boundaries of the screen.

My other question is about sizes in regards to 3d on a screen. My game is sort of tile based, is there a way to make objects appear to be a certain pixel size on the screen. eg 40X40 pixels. I'm sorry if this is a stupid question, I come from a flash background where most things work in pixel sizes. I'm trying to find a value that can have 5 tiles across on the screen. Or am I just supposed to play with the scale and camera properties.

Also while I'm thinking about it, currently I only have the indie licence but I intend on getting the IOS licence. Do I have to wait until I get that to start the project or does it just simply allow me to export the project for IOS. Can I upgrade to the Unity pro / IOS pro after getting the IOS licence if I feel i need it at a later date.

Sorry about all of the questions.

Thanks

The iPhone's resolution isn't 320 x 480, it's 640 x 960, although older models are 320 x 480. You don't set the screen res by number, you choose native/standard/HD in the target resolution in the player settings:

Target resolution

I'd recommend not trying to use pixel sizes unless it's really important to have pixel-perfect art, because there isn't one resolution, there are three (if you include 1024 x 768 of the iPad, and who knows if they might add more screen sizes for future devices). It's easier and still usually looks good if you use a high res and scale down, although there are downsides to that, such as using more RAM on devices that can't use high res anyway. You can start without an iOS license, but unless you have a good idea of the hardware limitations and input methods, you might make something unusable. You can upgrade to Pro later.

--Eric