Mono, your plants are looking quite healthy. I would ask if you have adequate drainage out of the cups - make sure there are a few holes to allow water to drain to prevent stagnation at the bottom of the cups. Also, be careful not to overwater; it sounds like you have it under control by waiting for the soil to be dried up; poke your pinky into the soil and if you feel no moisture add water. It's pretty tricky when you're in a small cup, but the good drain holes should help prevent overwatering.

As for the fertilizer, I've read a good rule of thumb is to wait until the plants are on their 4th or 5th node prior to fertilizing, and then only at 1/4 to 1/2 strength. I've burned up quite a few lower nodes by overfertilizing, so be careful and ease into it only once the plants are large enough to absorb the initial shock.

Good luck with your grow. I can't wait to see these lil' ladies poppin' pistils!