If you are trying to ask, What should be the minimum validity required on VISA to enter US -It should be before your VISA Expiration date on your Passport, it can be a day before also, but immigration officer in US has full discretion to take any decisions.
All Visas from all banks start with 4
Visas always start with a "4".
Yes, if they have a valid SSN# and a state I.D.
Visas for Indians can be found online with lots of information. The official Beuro of Consular Affairs of the US Department of State has relevant information.
None if you are a US citizen.
Some types of Visas available in Bahrain include Visit Visas and eVisas. Visas available for you in Bahrain also depend on where you are from and your nationality.
If you are outside the US you file a petition with the US Embassy for the country where you currently live. The US State Department has some information on non-immigrant US visas. USCIS is the agency that handles the actual visa processing. The US Embassy in your country will have the most detailed descriptions of the non-immigrant visas and how to obtain them on the Embassy website.
The word "visas" has two syllables.
Yes. They may obtain student visas, and attend college in this manner.
visas to stay and passports to visit.
Your question can only be answered if we know where you're going. Some countries require visas from US citizens, others do not.