Greenman101

After one has benefited here, you just want to give back when you can

UK police certificates are valid for a period of 1 year. On your PCC it should provide the Date of Creation (DOC), provided your interview takes place within 1 year from the DOC you should be fine to use it. Here is a link http://www.acro.police.uk/police_certificates.aspx where you will find the application form and further info for UK police certificates. For any other countries you have lived in, try having a look at the relevant country portals on Visajourney. Good luck!

It depends on how long the police certificate is valid for as stated by the issuing entity. Some countries are 3 or 6months while some are 1 year. Most embassies maintain it must be valid at the time of interview.So check with the issuing country.
For my country it is only valid for 3months and the NVC copy expires this week so my hubby has gone out today to go get a new one for his interview next month.

I'm not sure what you mean by this. I'm afraid you have to until the visa comes through. Maybe she could come to visit you in India or the UK, providing that country allows her entry?
Usually, yes. You will need to not overstay the length of trip allowed under your B2, and you will need to return to India (or the UK if you apply for processing there) for the medical and interview. Also, bear in mind that when you arrive in the US the CBP agent is allowed to refuse entry if he or she thinks you will try to remain the country. Others can tell you more about how to prepare for this.