Playing games at 500 points you don't have a lot of flexibility with Grey Knights. Your Psycannon squad could make some inroads on infantry if they stay at range, but I'd say your squad of 7 is going to get shot to ribbons before they engage almost every time. My only workaround at this points level would be swapping your Brother Captain for an Inquisitor Lord (+16 points) and lose two Grey Knights (+50 points), using your 80 point surpluss to purchase a 5-man Inquisitorial Stormtrooper squad with Plasma Guns (-70 points) to join your Psycannon gunline, and turn your now 5-man Grey Knights squad into an teleporting Fast Attack squad. You have ten points remaining to do with as you wish, perhaps give your Inquisitor a weapon of some sort.
Being that teleporting Grey Knights are the way to go in most games (they just get annihilated as footsloggers) the investment in Stormtroopers is going to be useful all the way up to 2000 points, and your Inquisitor Lord can always be demoted to a simple Inquisitor later if you wish.