I think you need to just stick with what you know best. Why not write back end services in C++ and create some services, that can be consumed with Java or PHP.

I think you need to just stick with what you know best. Why not write back end services in C++ and create some services, that can be consumed with Java or PHP. When creating projects/products.. your main goal should be to get it out to get feedback on wether or not people will even use it. I wouldn't suggest AWS for cpu intensive. I would suggest Linode, you can start small and just upgrade to large instances as needed.