So glad that he's hanging in there!
He will be VERY tiny when he turns into a frog. You're going to need to feed him pinhead crickets a fruit flies. An exotics store may have them, but your best bet for the fruit flies is to order them online. Worm man is a really good provider of them. One vial will produce thousands of little, flightless fruit flies!
My leopard frog is set up in a ten gallon tank. His substrate is large rocks, NATURAL, not painted- they're less dusty and less toxic. They slope uphill, out of the water. His water is about 4-5 inches deep. I currently don't have a filter, but I'm going to get one. The gravel probably isn't the best substrate, either, but it seems to be working fine.
He is always wanting to bury himself, so I provided him with a bunch of low fkae plants to hide in- they seem to be working fine. Make sure your guy has a way to hide himself... you don't want him to stress out.
You're going to want to dechlorinate his water, too. Whether you use a conditioner or let tap water sit out in the sun for 24 hours is your choice- I use water conditioner.
UV light is a debated topic with these guys- personally, I use one. I don't use a heater although I probably should. But this is what I've done and Comet seems farely happy.
Here are some pretty good care sheets. Take care, good luck.
http://allaboutfrogs.org/info/species/leopard.html
http://exoticpets.about.com/cs/frogsandtoads/a/leopardfrogs.htm
http://www.anapsid.org/leopardfrog.html