Is 500 ppfd on new seedlings ok?

Don't forget that it's not only light intensity (PPFD), time also plays a role but 300-400 is an OK amount. Seedlings "can" be started in low light like many recommend but out in nature many sprouts first light is full sun and they do ok. I will sometimes lower the light level if I want to get the plant to stretch a bit more and increase the spacing between nodes which makes low stress training easier. If there is a lot of light the plant, depending on genetics, may grow shorter and stockier than you would like but can be a good thing in a small grow space.