In my experience:
1. Speakers are really good for standard ones. For some reason they sound louder/better when playing music through bluetooth rather than aux, at least in mine.
2. Engine sounds lovely when giving it the boot, lovely 3 cylinder rumble, otherwise very quiet. Exhaust note is non-existent, consider an aftermarket system if you are after that sorta thing.
3. I average 45mpg, mostly around town with the odd blasts down some A/B roads. So that's like 400ish miles to a tank?
4. Depending on price per litre obviously. Around £50 should see you full.
5. Again depends on prices locally. Round my end rear 3 windows cost £90!