It depends. If your wife is already in US and if she already has H4 status, then you need to show her I-797 (her h4 approval notice issued by USCIS) along with your docs. But if she is applying directly from Nepal and has not been here in H4 status, then you need to produce your marriage certificate and other evidence of marriage(optional) to the consular. In any case, having a bank statement with balance enough to cover your dependent's expenses would help. There are no requirements for all of these, so I cant suggest you the dollar amount that you want to have in your bank statement - my guess is around 7,8 K would do. Again, these are all to be in the safer side - there are high chances that you may not be asked to produce any of these....