1) Yes, P527 has a today plugin for easy switching between silent modes, and it can even automatically switch modes according to calendar events. 2) There is no voice recording application bundled, however you can find freewares and commercial software for this purpose. You may also record on your PC, then use it in P527. P527 (And all other WM6 devices) supports wma, mp3 and wav as ringtones. P527 additionally supports mid, amr and aac. 3) The speaker should be loud enough for listening from the car. 4) Yes (WM6 common).
GPS and Wifi uses different radio modules, it doesn't interfere with GSM radio. For radio use, I am not able to test here, so I can't tell you how it performs when there is incoming calls.