First time and small batch biryani
Look around in the areas with the South Asian community (Pakistani/Indian/Bangladeshi) to find ethnic stores for specialty spices.

Whatever recipe you use, reduce the ingredients proportionately like you would for any other recipe.

The only reason for a large pot is to make it easier to mix the rice and gravy after it's cooked. If you don't have a large pot available, you can use a wide pan (of adequate height) with a lid. Avoid using narrow stock pots. It will be difficult to mix the rice up in a small pot without breaking the rice.

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You can even find boxed spice mixes in the ethnic stores to save the pain of buying individual spices. You can find these on Amazon as well.