No need to feel stupid, everybody starts somewhere.
Atelomycterus macleayi would do fine in a 250 gallon tank as long as you make sure it is around 5-6 feet long and 3-4 feet wide. Though some say it can do well in something as small as 4 feet long by 2 foot wide, I feel the shark could and should have more room.
White tipped reef sharks need at least a 2500 gallon tank, but I have an obsession with them so I'm quick to say it would be cool to have one even as a juvie when people mention a ~1000+ gallon setup.