Saw your bike over in the recently bought thread coors. I have its younger brother, the Trek Fuel 90 large frame. Upgraded discs all around, sid air or whatever its called front shock. Very happy with it, i have had it for a number of years now.
Clip-less pedals..... what a can of worms... I recently upgraded to them, and love them. But, i have been riding for a number of years and have the experience to take advantage of and appreciate the different advantages they give you. For someone just getting into it, or back into it, i definetly recommend flat tops. Though for just starting you picked an awesome bike
Take it easy, start on the easier less technical trails, get your fill of unadulterated speed, then move on the technical trails once you are confident you are in control of your bike. Best advice i ever got on technical trails is this: FORGET the back tire, ignore it, so long as your front tire is going where you want it to go you should be good.
That and fight the urge to slow down in rough spots. If you have ever watched a child's spinning top you will know that you can bump it and it will right it self, think of your tires like that, if they are spinning fast enough they will keep your bike upright enough for you to keep going. Plus if you float the first root or rock at speed you will go over the next few, but if your going slow you have to float each one.
Most importantly find some good riding buddies and have fun.
Oh and wardozer aint lying, find some good gloves, or you will bust your knuckles all to pieces when you wreck, and you will end up with lots of blisters inside your thumb. And forget open finger gloves, not worth it.
Feel free to ask about anything i love this sport, and wardozer above as well(though he appears to be doing street riding), and its great fun to help someone else get hooked.
Oh and a note on street vs mtb riding, if your going to ride a mtb on the road increase the pressure in your tires, same idea as wheelin softer tires have more grip off-road but wear out quicker on road, oh and lock your back shock out if you can otherwise it will be absorbing half your effort.