Levels are based on adding extra difficulty -- always based on the number of features performed.
Grades of execution are based on quality.
So you're right that skaters can earn more points by spinning faster and with more attractive positions, but those extra points would come from the GOE, not from a higher level.
A backward spin rotates away from the leg on the ice. For a counterclockwise skater, that would be on the right foot, spinning to the left.
In general backspins tend to be more difficult, and especially in the layback position.
Almost all laybacks you've ever seen have been forward spins. This is especially true in the required short program layback, which doesn't allow a change of foot.
Occasionally skaters go into a laid-back position on the backspin foot as part of a combination spin.
Here's a rare attempt at a backward layback (layback position in a backspin to earn the "backward entry" feature as well as the change between sideways and layback feature.
If you happen to know ballet terminology, forward spin = en dedans/inside pirouette; backspin = en dehors/outside pirouette.