An Idea I have heard being thrown around is 6 Night Goblin shamans all level 2. You get every spell in the lore, and 6 castings of d6 str2 no armour saves allowed. In terms of Wolf riders vs Spiders it depends on you really, I prefer Spiders for the terrain bonus, and spiders are more killy than wolves. For an anvil unit a great big unit of Goblins can work with steadfast. The problem is, there isnt to much that is killy. You could bring squig herds and or riders, if they make it into combat they are pretty good at putting the hurt down. But are fairly expensive for a goblin army. Definitely bring war machines. Bolt throwers and rock lobbas to hurt the other big blocks and elites. Hope this helps give you an idea!