I am a not a professional to creating things
The Arduino is for hobbyists. But, it does help if you know some electronics & programming.
The Arduino can actually be good for learning beginning programming.
It's probably not the best way to learn electronics, but since the Arduino is already assembled and there are lots of plug-in "shields", you can do a lot without knowing lots of electronics. Still, it's better if you understand some basics like Ohm's Law and if you understand what common components do, etc.
I suggest you start-out with a basic-simple audio player made with an [u]audio shield[/u] and see how it goes from there.
I'm not sure about that. The "standard" Bluetooth modules used with the Arduino are not fast enough for audio streaming, or maybe the Arduino can't feed it fast enough.
That's going to require an operating system and I don't even know if it's possible. "As shipped" , the Arduino is a USB device, not a USB controller.
It depends on how "compact" you want it. The smaller you make it, the more difficult it gets and surface mount micro-electronics is super-expensive in small quantities. The costs go down when you mass-manufacture and automate production.
...You didn't say anything about a display.
Or, maybe check out the [u]Raspberry Pi[/u].