It sounds like B.J is settling in well!
He's behaving perfectly normal for a baby budgie
Babies tend to like to wedge themselves in small spaces because it reminds them of their nestbox they used to sleep in. They love digging around in food dishes for the same reason--small, enclosed spaces make them feel safe.
He'll grow out of doing both those things, though, not to worry. If you don't like him tossing out his seed all the time, you can get him a different type of feeder for now that doesn't allow him to get completely in, such as a ceramic crock like this:
Or a silo like this:
It's funny that he tries to do flips!
He's just clowning around, I doubt he could break anything in this manner, so don't worry.
Also, as he gets older and more independent, he'll enjoy going up to the top of the cage more. As babies, budgies aren't too comfortable venturing up too high just yet
Best of luck with darling B.J! Keep us posted on how he's doing