I started mt. biking about 10 years ago, although I too have been out of the saddle--almost 5 years for me following the birth of my son. I vowed to get back into it this year and have been really enjoying myself rediscovering how much I absolutely love being out on the trails!!

Regarding your pedal question: I would go straight for the clipless pedals. You're a roadie, so I'm assuming you're already familiar and comfortable with clipless. You'll reap the same efficiency benefits mt. biking with clipless that you do on the road. I'd skip cages completely. They're not as efficient as clipless and if you miss getting your foot in a cage at a crucial (i.e., technical) moment, the cage can spin around so that it is now dragging on the ground and could scrape and catch on something and send you off balance and down onto the ground--something I personally learned the hard way when I was first starting out oh so many years ago!