1) You're a beginner, moving to intermediate. It isn't so much about what you are, but what you're gonna be. To get your 360, jump first, then pull the handle to cause the spin. If you do this, you will get the handle (and be intermediate!
). Right now, it sounds like you're hucking a spin and then trying to catch the handle. Don't do that.
2) The number of fins does not really matter. The agressive 3 stage rocker boards (i.e. Parks and LF Subjekt) are probably a bit too advanced for you. Other than that, most of the current boards out there will serve you well. Since you're looking for a continuous rocker, I would definitely try the Liquid Force Team board. I prefer continuous rocker and love that board.