1. Can she file DV case(false) after one year of separation in India? I last met her in India about an year ago and then I went abroad and she decided to stay with her parents.
She can very well file a DV case after one year of separation too because it is a continuous offence.
2. If I file divorce in USA on irreconcilable differences, what kind of risks I may have with my wife who may seek 498a, nri women's cell help, passport impounding, extradition, Red corner notice, Look out circulars etc.. and how to face them?
Filing a divorce case in US will not have an impact to your marriage solemnised in India as per prevailing laws in India, especially when you attempt to get an exparte divorce in US. This will not be considered as valid divorce in India.
If she lodges complaint against yo for the offences of cruelty and dowry demand harassments etc., the police shall on receipt of complaint, try to locate you, if that is not possible, they will register the case and keep it pending, or in case of pressure from higher officer or in return of the graft received, they may move this file to Court and seek court's permission for issuing look out circular. Neither Court nor Police has power to impound passport. The procedure for impounding passport is clearly given in section 10 of the Passport Act, under which this reason is not included. Red corner notice cannot be issue under this circumstance.
3. she lived with our family for hardly a week in India, do they still need to be worried about the false 498a case with the new supreme court guidelines?
If she has decided to include your parents in the case, there is nothing that will stop the police to conduct inquiry against them too. The police if on inquiry found that they are innocent and no cases found against them, they shall not be impleaded in the case and their names shall be deleted from the charge sheet. The supreme court guidelines is actually instructions to police/investigating agency to conduct proper inquiry/investigation before filing charge sheet or making an arrest into the alleged offences.
4. How do I know from USA if my wife has made any complaints or FIRs with police in India? I am afraid when I come to India, the police arrest me at the airport.
The police will not arrest you at the airport, they have some other job to do instead of waiting for your arrival and arrest you. In the event of she lodging a complaint with the police, the police will certainly call you over mobile, if there is no response then they may contact your parents, by which you can come to know that there has been complaint lodged against you in the police.