If you are going to use slick2d you have to keep in mind that it isn't going to work on Android, so if you really want that look for another library.So I guess a library or sdk will do the graphics thing for me or at least make it easier? Also would you know if that could be implemented for android if a library is used or would that be library specific?
unless you know really much about graphic hardware and stuff, it's really hard to make a game, library or engine. And yes, java is a good language!
Because this is the first game you are making its better to just focus on getting a game working and worry about making games for phones, like android, later.