FYI, Chris Hildenbrand has a number of (mostly) free tutorials and game art assets on his blog, including some of the graphics from this game [1].
[1] http://2dgameartforprogrammers.blogspot.com/2014/02/top-down...
[1] http://2dgameartforprogrammers.blogspot.com/2014/02/top-down...
The sounds were purchased from http://audiojungle.net/ The whole Envato network has great resources for developers.