Is this a scam?Please help me.

No legitimate employer is going to tell you you have to use a particular travel agency to get a visa. Visas are issued by embassies or consulates, not travel agencies.

If he's using Gmail, how do you know he's in Brooklyn? Gmail hides the IP address.

Here is a good indicator sannoca. Scroll to the top of the this page and type, consultant.com into the site search. The results will amaze you because it has been used in countless scams before.