Young plant with drooping leaves

First mistake was using old soil.........new plants, new soil..........

What's the manufacturer's recommendation on the lamp distance/power?

I'd say a bit on the hot side, try get it max 28c. humidity needs to be higher if you can, ideally around 65% - 70%. light at 500 is a bit intense, try get this to around 200, 500 is for when the plant has matured and is in the veg stage (3rd week). the drooping yellow leaves could be over watering. If you can make all these adjustments, or some at least, you should see some improvements. Also give some nutrients, nothing too intense, you want nitrogen for leaf growth and phosphorus for root development. hope this is helpful. Cheers.

Too much light, too low humidity. Raise that humidity to at least 60% but maybe even up to like 68% They want the high humidity right now