The reason why I suggested Webstorm is because it’s similar to Android Studio.
(both are based on IntelliJ’s IDEA)
A drawback of Webstorm however is that it is not free (paid application). If you don’t want to pay then I’d suggest you just go with a text editor like Sublime Text instead of a full IDE.
As for learning Ionic 2 (and Angular 2), just read blogs and work through some tutorials, there is plenty available on the internet.
(regarding Ionic 2 and Angular 2: you should probably learn both at the same time although Ionic 2 tries to be a “wrapper” aiming to simplify Angular 2 and shield the developer from some of the complexities of it - so you can get away with not knowing all of the intricacies of Angular 2)
Here is a list of some useful resources:
The official Ionic 2 documentation (very good):
ES6 and Typescript: