Re: how much experience do I need
Dylan Winter posted a link to a youtube record of a Brit who bought a $4k boat and sailed it from New York south. There is a well travelled and protected route south once you get past New York.
I would get an experienced skipper to help you get past New York. Once into the protected waterways you should manage on your own. You should have learned enough by then from your skipper. It is not rocket science. Pop out for an ocean leg when you feel ready.
BTW your plan to sail down ONE mile off shore is DANGEROUS. You will have onshore winds most of the time that means a lee shore. Anything goes wrong and you are on the rocks in minutes. The further you are from land the safer you are.