@Binod: PCL's in general are platform independent so that is why you have a limited subset of the .NET Framework. You are always free to use linked files or the new shared code projects as well. If you want to stay in the PCL world there are some nice ways to add functionality like I did for HTTPClient in some of my later demos. For encryption take a look at the PCL Crypto library: https://www.nuget.org/packages/PCLCrypto
@pasniak: To use Visual Studio you will need the Business Edition which is part of the 30 day free trial as well. After the 30 days you will drop down to starter which limits the app size. This app is much larger and has a lot of components so it does exceed the app size for the starter edition and you would need at least Indie. You can always email in about extending your trial though.
@Mattias, you can absolutely use MvvmCross. For this series I just focused on the core out of the box experience when creating apps in C# with Xamarin. I have a log of MvvmCross examples on my GitHub as well.