1) A pod will help with better flow in the top end and it is recommended to put it in a box or adding a headshield with a cold air feed from the front bar or something similar. Depending on where you live, a pod could be illegal ie. defectable.
2) A better panel filter in the stock airbox works great since it is already fairly shielded from the factory but may not be as great in flow in the top end then a pod. This is legal.
3) Don't know if there are any single bolt on kits that include pod and box but these can definately be bought separately and combined. Try nismo.com.au or even knock a box up yourself!