For Goffs, you've only really got 1 unit making good use of the klan kulture. Grots can't use it, the weirdboy is so-so in combat anyway, and the big mek is going to be shooting. You also have a lack of defence, your army is quite squishy! if anyone brings a dread and the dread gets in combat with the boys, it's only your SAG which can try and save them, and they will be falling back to do it, so lose their ability to charge or shoot - not ideal!
I would consider either Bloodaxes (so the bys can fall back, SAG can shoot, then the boys charge in again) or Deff Skulls (for the improved reliability on the SAG and a 6++ on everyone). With 30 boys, you can expect to kill most infantry quite efficiently, but as people have said, not so much if you fail the charge.
To complete the 500 points, I wou certainly avoid using any vehicles, as they will present a target for anti-tank and will always be killed early. with 84 points to spend, you've enough for a second Big Mek with a SAG and a grot oiler to go with him. The extra firepower will be very effective, especially at low points, and the oiler will be useful to soak up any snipers which may appear - and if you play the same opponent regularly, expect them to appear if you're bringing 2 SAG's!
You can also spend a CP to make your list a Dread Waaagh!, which then allows a Mek (being the warlord) to take the Souped Up Shokka, and gives access to a "shoot twice" stratagem for the meks, which means you could output 5D6 S2D6 AP-5 Dam D6 shots per turn with just 2 models!