Open sourced is often much easier to make cross platform if that might one day be the goal. Developing in Java or something else that works cross platform could be a solution. If you are complete beginner then open source will usually be easier to find documentation and help with via the open source community.
I personally switched from iPhone to WP7 and could not possibly be happier. As awesome as I know WP7 is the market still isn't totally there for it just yet but having looked into developing for IOS, Android, and WP7 all individually. In my opinion WP7 is the easiest and I feel like the Android tools are poorly coded but you will have a big community to help you along the way.
Considering the help of the community and the size of the market share that Android has right now I would say open is probably currently the best bet but I would not develop for Android and not WP7 personally. Cross platform apps are where it is at now a days.
Nice question, I used to ask myself everytime, untill I found that the best way to share something you've built is by having others recomend it, the more the best, and the fastest way to have that is if your application is free. Now the real question is even if your application is free, shall it be open or closed source, let's say that it depends. 1.
Closed source - If you yourself are a programmer and/or you have some good programmers to help you out, and mainly if your application is not so complex let's say you can build it from zero to open beta in less than 6 months, than it means you can keep in touch with it fix bugs, adding some new features, and finally you can some day make some profit out of it by having advanced features, or something. 2. Open source - Keep in mind that when a user/client hears open source their eyes shine while they think "if this application does what I need, i'll find it really nice to never have to pay for it".
Open source most likely means "never ending project" atleast untill some one decides to rewrite it add new features and make it obsolete, so you have to choose well if you want to follow this path, since moslikely any profit from it will be from donations, and depending on your personality you can't be selfish and keep all profit to yourself since there will be many others contributing to your project. Has for to solve your problem on wich plataform/programming language, you have a good option, JAVA, it is the more eficient crossplataform language, and than to rewrite it to android or other, it will take lessa changing in your code. Hope to have helped you.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.