Maybe a bit old-fashioned, but I take an old awl and my hammer to rap the metal studs at the screw locations. Even with a lot of screw locations, it just takes a couple of minutes and give a perfect depression so the screw doesn't wander.
I'm with BIG on the screw choice....fine thread Gripper brand screws are what you need for attaching the drywall.
You had also asked how you attach drywall to the bottom part in another post....what is your span? If it is under 22.5", then it is no different than attaching drywall to 24" oc studding, but of course the less distance the better. You can also nail in 2x2 strapping as struts to bridge the gap every so often or notch a 2x4 with a jigsaw on both ends to bridge the gap, give you another attachment point and add a bit more strength.