As for marketing, if that's a Windows app, The Windows Marketplace is quite a good resource.As a matter of fact, the advantage of the windows marketplace is that you don't actually have to promote it.People will check it eventually.You just need patience.If your app is available for all the main platforms, then you probably won't have to worry much about promoting.Although, a helpful thing would be creating awareness about it on Instagram.Instagram is so right for these things.Another important thing is if you can discuss about it spread a word on App Devoloping forums or websites, that will knock some attention.