The chakras are already organized into groups: Least (Crown, Feet, Hands), Lesser (Arms, Brow, Shoulders), Greater (Throat, Waist), Heart, and Soul. There's a little inconsistency in that Incarnates get access to Crown alone at 2nd level, and possibly some of the PrCs might have a little oddness, but otherwise the 3 base classes and the Access Least/Lesser/Greater Chakra feats all agree on the groupings. Those groupings are somewhat more like invocations (Least/Lesser/Greater/Dark), rather than spells' levels.
Note: The chakras are ordered in power (or at least the level at which they're gained) based on their proximity to the center of the body. Outer chakras are low-level, inner chakras are high-level. Waist being low-level makes no sense like that.