1) Yes, the bouncing is called 'popcorning'. All baby mice and rats do it, some moreso than others. It's so much fun watching them bounce around.
They'll outgrow it. But, be careful when handling them in the meantime obviously, they'll pop out of your hand for a fall to the hard floor quicker than you can say popcorn.
2) If they are boys, then most likely not. Male mice are very territorial and will often kill each other. There are exceptions, as some of our other mouse owners will tell you, but it is unlikely, especially considering they are not siblings raised together. Females do well in colonies as long as you introduce them properly.
Just an obvious warning though: If you get females later on, don't ever put them in with the males, even for a minute. They mate with incredible speed, and easily have 6-20 babies in a pop. That would be a separate cage purchase for each baby male you might have, and possibly the purchase of a larger tank for your females. You could easily end up with a wall of 20+ cages before you're done from one five minute 'oops'.
3: Probably. Mousies love their wheel. He'll probably warm up to it before too long. Give him time.
4: It's just different personalities. I had a little girl who loved to sleep on top of her water bottle. Another who was quite the little house keeper, constantly rearranging her bedding. You'll find they do have very distinct personalities. Some nervous and bitey, some fearless and calm and anything in between. It's my favorite thing about watching them!
And, please, ask all the questions you can come up with! I'm getting rats and have asked all kinds of silly questions. I'm often surprised at how non-silly they actually turn out to be when I get my answers!
Post pictures soon! We lufs fuzzybutts!