flyin97formula

Ok so I just bought this car, first f-body, and I was told the check engine light was on because one of the O2 sensors was bad.....well I just had the computer scaned and this is what they told me
p0719 - brake switch circut low input
p0440 - EVAP small leak or something
p0420 - catalyst system efficiency for bank 1 is to low
p0100 - MAF or MAP malfunction

the car has an after market ypipe but still has cats, and a slp intake system. other then that it is stock.

Is there ONE problem that could fix all these codes?
please tell me what I need to check/fix to get these to clear because I have to pass emission asap

thanks for the help