If I were you, I would just spend some money and get a professional template like http://templatic.com/cms-themes/iphone-app which is specially for you to sell apps. (It's a wordpress theme)

This particular theme may not suite your genre of app, but I'm sure on the internet there are many. Also as for promotion, maybe you would like to contact freeappaday.com which does promotion - but you would have to offer your app free for a few days.