Hi, have been to the NW200 a couple of times found it great to be so near the action. This year the entertainment starts from 13--19 May. Decide which races you want to see using the official website
www.northwest200.org which also includes a map of the circuit. Cant help you with the camping sites but Nutt Travel can help get ferry tickets. I used to go on a Thurs or Frid and return on Mon, less conjestion on the ferry. For viewing I suggest initially at Portstewart. From there you can then walk back to the start area passing the paddock and pit boards (which are not in the pits) Going the other way gives a good view of York Corner and further up Mill Road roundabout.
Hope this is some use to you, and the weather stays kind.
K.T.R.O.T.R. regards Dan