Hi, hopefully I can help answer some of your questions.

First off, you probably should have given your new snake a couple weeks to get used to his new environment and unwind. Moving to a new environment is particularly stressful to any snake, but especially to Balls who tend to be more sensitive to changes.

I would find out what the snake was eating while at the pet store, or if they know what the previous owner was feeding him. If it was live rats, then stick with live rats. At least until he is eating consistently and then you can try to change to F/T if you'd like, but don't be surprised if he gets picky again. Balls are imprint feeders and tend to stick to one type of food all of their lives.

I wouldn't try to feed more than once a week. Introducing prey items is actually stressful to the snake and if you introduce one too often, the stress may be causing him not to eat. One feeding attempt a week is plenty... they can go months and months without eating, so there's no need to worry about him starving.

Finally, you mentioned that you tried all sorts of different prey items and left them overnight. That might be okay for pre-killed or F/T, but you should never leave a live rodent (larger than a rat pup or mouse fuzzy) in his cage overnight without risking serious damage to your snake.

It sounds like he's a decent eater, but just needs time to get used to his own environment and placed on a static diet. Stick to one food item such as weaned (or very small) live rats, and offer it to him once a week. Before long he'll be waiting for you on feeding day.

Good luck!