So do the minums from the leafcutter colony do tile making as well as used fungus material disposal. Which means the minors are used for getting to smaller plants. So the medias and majors tackle bigger plants? Or am I getting everything mixed up?
No - the minors do tile work, not the minims. In effect minors are the equivalent of the workers from current levels.
Minims never leave the nest and are not directly controllable; they take leaves from the drop-off chambers to the brood chambers where they become fungus & take waste to the refuse chamber. You'll get a free minim with every minor / media / major tile.
Mediae are probably the most efficient leaf collectors for cost vs. effectiveness. Minors can carry leaves, but suffer a slow de-buff when they do. Majors can also carry leaves but their abilities make them better used as fighters.