Tilemap system for both iPad and Iphone

Greetings,

How can i build a level from a tile map that perfectly fits into a iPhone and iPad universal game, assuming that any pixel away from the original level concept can simply destroy the game design ?

I mean, a perfect level design for the iphone should also be perfect for the iPad and in consequence on that, it must meet the specifications of the game design document (things like physics, collisions, checkpoints and everything related to the puzzle elements)

And lastly, I would like to clarify a doubt regarding the platform.
Today we are in two programmers, but only I own a MacBook. Therefore it is possible all that was mentioned above is “simulated” in a windows based application and only when the game is ready, we just port it to MacOS?

The correct way would be to create a win32 application with the resolution of the iphone and the other with the resolution of the iPhone?

Best Regards.
Max.