Separate tanks are actually ideal - pet stores house them together because they have limited space and don't plan to keep them for long. Make sure his hides fit him snugly, and definitely add a few more in there. 55gal is enormous for even an adult BP, but you can make it work if you have enough "stuff" in there to keep him from feeling exposed. If he doesn't eat after a couple of more weeks, I would set him up in a 6qt or 15qt tub until he is a more established eater. Make sure you feed in-tank to avoid stressing him by moving back and forth (not in a separate enclosure). Your average (aka ambient) temp should be ~80deg, with a hot spot on one end at ~90deg so he can choose what temp he prefers. Oh, and he can definitely go up in size for prey. Mouse pinkies are typically too small for the smallest new hatchlings. You can also increase feeding frequency to every 5 days until they hit ~500g or so, then drop down to weekly.
The easiest tool for caring for BPs that many people forget about is a digital kitchen scale. Monitoring weight (and writing it down) will let you know if there is a problem when they don't eat too long, as well as help indicate when to go up in prey size (10-15% of body weight).
This is a great resource on this site to check your setup and husbandry against:
http://ball-pythons.net/forums/showt...ius)-Caresheet
Good luck and welcome to BP.net!