A 15 gal (24"x12"x12") is good for a pair, but if you can afford it go a bit bigger, incase you expand and get more leopards.
Feed can include: Crickets as main; meal/king/superworms as secondary; waxworms silkworms butterworms as treats and the very occasional pinky mouse (I don't use them myself)
To fatten them up, try feeding them 3-6 waxworms a week, with the odd silk if small enough and butterworms if you can afford them. At 4" they are still very young juviniles, so best bet is 3 week old crickets if they are big enough for them, mealworms, and waxworms. Slowly move to larger items as they grow. I believe the rule is don't feed anything longer than length between tip of nose and eyes. (anyone else agree??)
Also I have a caresheet if your into a long read
http://www.freewebs.com/albertabredg...s.htm#36067187
Hope it helps you out