I would just use a metal edging that you beet down a few inches and pin it from the inside. Then place in the gravel. It does not need to be leveled out. It will hold the rocks and the edging can be bent to go with a more curvy or formal design.
I'm trying to imagine the look of the gravel though. The color of rock, type of rock, and so on all makes a difference in look and cost but that's most likely the best option for you based on budget and experience. It can be done very simply or very complex.
You could go as far as notching into the slope at various spots and putting in larger stones. Then running the metal around those, in front or behind, with some more naturalistic curves. Then place in medium sized stones of a different color and finally add in gravel. It would be the same look but more on the design end. Then tuck in some simply ground covers to help hide the edging and give the overall look a more natural feel. You definitely want to keep the slope away from your house though. As for draining, just simple 1 inch pvc pipe can be placed every few feet with the slope moving towards them. Wrap the ends of the pipe with burlap so they don't clog. Have some ground covers hiding the face of the pipe coming out on the slope.
