First off a reciever is not a motor controller. The receiver is what sends signals to the ESC. So you still need a motor controller.
You could use that battery to power the motors with a correct ESC or something else. The BEC would be used as a voltage regulator to power the receiver, if the ESC does not have one built in, and any other electronics considering they do not draw more amps than it can supply and run on 5v.
You want to go ask questions at this forum: http://forums.delphiforums.com/THERFL/? It is the Robot Fighting League’s home where all the builders post progress reports and ask their questions. There is also the RFL facebook page (https://www.facebook.com/BotLeague), but the forum will get you better answers.
Or if you want to do some learning on your own time, there is http://totalinsanity.net/tut/novice.php That link takes you to the novice tutorials. They also have some more advanced stuff.