Youre doing good. Some advice: The 100w are an ok amount (more can never hurt). The drooping is hard to say, first guess is not enough water, second is too much water and third guess is too high temps. If youre watering until it drains out the bottom and then waiting until the pot feels relatively dry then you are already doing it right. How hot is it at the TOP of your plant? What does your cabinet look like, can you show a picture of the whole setup? Do you have air being blown out plus a hole for air to come in? You said you are waiting until the plant takes up half the height of your space until you switch to flowering. However, your plant will grow about 3x its size after going into flowering PLUS dont forget you need some space between the plant and the bulb. Sounds like you should switch to flowering asap but its hard to tell without a picture of the setup. My guess is you will have to tie it down anyways since it will outgrow the space.