Take a look at the beginner's guide tutorial
that will give you an idea of the workload required.
For your first question you don't really write code (as in a coding language).
Developping for iOS is the same as developping for a regular browser for a desktop computer, you just have to use the touch object for inputs (instead of mouse/keyboard object) and be sure your project has the correct size settings.
Construct2 only works on PC for now (there are tips to make it run under linux and/or mac though) but still can export multi-platform projects.
Check the various tutorials, they should answer all your questions and be sure to download C2's current version to test it out, that's the best way to answer most of your questions.