The biggest hurdle was actually trying to create a native form; something which is remarkably difficult to find good resources for compared to other things.
Had I tried to learn in my own time, without the pressure of having to get something working at all, I would have spent months reading textbooks and learning how to write basic hello world apps.
Instead, I made more progress than I could ever have imagined just by being given a challenge and an idea of what to make. And that's sometimes the best learning experience you can get.
However, it did have in-app purchasing and that was tedious to implement.
Not code-wise, but fiddling with xcode/apple dev center to generate ad-hoc profiles and signing and transferring to the device.
That sucked up more time than the code, at least for the first prototype build.