This line is in reference to a song by artist Joe Jackson. Jackson's best known song would be "Steppin' Out." Kanye proceeds to rap, "Now, I'm mad, real mad Joe Jackson", which translates to "I'm mad, so I'm Steppin' Out".
Slick Rick is an 80's rapper. His song "Hey Young World" conveys the message that even though its cool to be a hoodlum, you should try to make something of yourself. West is saying she should leave Ne-Yo because she's better off with him.
this seems to be a racially offensive statement, as "casper" is sometimes a derogatory term for a white person (after casper the ghost) - Kanye seems to be asking if this woman can see past her white admirers to choose him instead.
keep pursuing what you want (by putting down others, which in turn raises your confidence), whether you're rich and wearing expensive Louis Vuitton clothing (as in Vuitton/button -ing a shirt up) or of average wealth and wearing affordable Reebok shoes