Welcome to the Buzz and kayaking! I had a similar background (sea kayaking/rafting/yakfishing) prior to whitewater. Advice: Sell all your other sporting equipment (golf clubs, bowling ball, tennis) on e-Bay, because this will be the only sport you'll be interested in from now on. Keep your mountain bike, you'll need it as a shuttle.
I am a big guy (6.1, 205) and like the WaveSport Super EZ. It easy to learn in and covers river running and basic playboating. Good combo for starting out. Super comfortable. Rent first, buy later.
Get as much pool time as you can possibly handle. Playing at the pool sessions is safe, warm, and you'll meet others who can show you strokes, rolling techniques, and gear. Great learning enviornment. This will transfer skills to your lessons at the end of May. CWWA Pool sessions are Sundays 3-7 at the Meyers Pool ($6.50), 80th & Wadsworth (Carr St). Search the buzz posts for other pool session listings. You'll be set for a great summer.
See link: http://coloradowhitewater.org/