Well, Black has different options. But I wouldn't play ...b5 as it blocks the bishop's pin on the d3 pawn that Black just created.
Something like this comes to mind:
Playing with the tension on the d3 pawn, and then also finding another point of activity: the f4 square.
Knight to e5 is a maneuver I avoided when I was lower-rated, as I didn't like "doubling my pawns". But doubled pawns in these kinds of structures can often be useful - they can help restrain your opponent's pawns from advancing, and can open useful files for your rooks.
 
     
     
     
    
 
    
what happens after though? i just push b5?