Shah jeera is a fine cumin which is used mainly for biryani and masalas. If you don't have it then just omit that. Do not substitute regular jeera/cumin instead.
To roast the cashews in the microwave, apply some oil or ghee on the cashews and cook it for 40 seconds to a minute.
You can add ghee/clarified butter in additional to oil or substitute oil with ghee completely. Ghee definitely adds more flavor.
Additionally you can also add a pinch of saffron to 1/4 cup of warm milk, let it stand for a while and then sprinkle the saffron milk over rice after final assembly.
You can use store brought fried onions or sauté sliced onions in oil till it turns brown and caramelized.