Isla Blanca Park on South Padre Island is the best public spot you can watch from (IIRC it's 3 or 4 miles from the launch pad) and it's an amazing experience, highly recommended to anyone who's able to make it out.
I believe they clear out the launch site within a few kilometres so nobody gets hit by random concrete debris or just melt away, literally. The control centre is probably invitational.
But you can freely watch them live on Twitter. Just follow the official @SpaceX account.
Yes it's open to everyone. South Padre Island would be your best bet.
So is the Gulf, except in the areas closed by the notam.