I just purchased a Pahntom3 SE drone and I am trying to register it.  There are so many sites out there, how do I know which ones are legit?  Any suggestions on a website.  I am using the Phantom for recreational purposes.

Start here and enjoy the new UAV.  https://www.faa.gov/uas/getting_started/

Thanks for the help on 2#, furthermore, you can visit this site for checking the drone regulation in the US.