You can pretty much use the MGOCPM straight out of the bag. I've done it with one tank, and after a couple months a few bigger pieces of wood/bark appeared on the surface.
Didn't really bother me, but I sifted it for the next tank.
The only real prep I did was sifting out the really big chunks, and putting the MGOCPM in a bucket and adding some water to it the day before/that morning. My stuff had been sitting around for a year, so it had mostly dried out. If your's is fresh/moist, this is probably unnecessary.
As to the driftwood, I'm a big fan of bolting them onto a slate tile - it makes sure the wood doesn't float, and gives it some stability too. Although, it doesn't allow for much manipulation/modification, so figure out how you want it before you bolt it to the slate.
As to set up, I'd stick the wood/slate on the bottom, add your MGOCPM, push it around and try and get it properly distributed and as much air out as possible. Add the cap, plant, mist with spray bottle, and fill.
I'm not certain about how to handle a hill in a dirted tank, I would think you would want to use inert material for the bulk, but not sure aside from that.