1) This works better if you have more resources. so less widgets and more ram available. Some firmware also work alot better. If you are confortable with rooting etc then you should check out the stock II8 and tweaks that go with it. If not you'll just have to put up with it for now.
One thing, just to save your sanity is to tap lock, wait for screen, then press again. This prevents the frustration of when you hold it for a long time and nothing happens!
2) There is another thread on here about that, it may be an interferance problem from the GSM. If you got it from your carrier, try a factory reset to rule out any software problems, and send it back for a replacement. Its caused by bad shielding
Its possible it is a sw problem too, so try a factory reset first.
3) The music should stop when you get a call. Check the jack is pushed all the way in. Some galaxy's don't connect properly aparently. Also are you using the default music player? Push the headhphones in and out a few times. It should make that blinggg noise every time it detects they are removed on plugged in