not sure you need c++ for your project
My experience with C++ (using Marmalade) is that if you need a lot of UI, than you are better off with the Java framework. Designing UI with Marmalade is a real pain. It's great for power hungry games and apps, but not for UI.
If you absolutely need to use C++, my advise it to start with the native Java and NDK, and only if you're not satisfied, look elsewhere. Even in Marmalade, which is supposed to be cross-platform, you will reach the point, too quickly in my opinion, in which the SDK doesn't give a cross platform solution to what you want (say use a downloaded third-party sdk, or request some OS function that the SDK does not offer), and you will have to implement specific OS "EDKs", so will have to know your native coding anyway.