Big lights

You want 400 ppfd in this stage (up to 600 ppfd with CO2). Look up a "ppfd map" of your light. Put it at the recommended level and leave it. You can save a lot of electricity by dimming it but you need a lux meter at minimum or a PAR meter if costs don't bother you. Without measuring the lower power somehow, you won't know if you're getting the right amount of light to your babies.

That should be a good distance. Keep an eye on them.

If you can switch low the dimmer at 20% for first 10 days at 16 inches. After follow the 16 inches whit maximum of 30/40% of light power. Try to see the manufacturer directions. 👍