[Gimik]

Turning off the screen while in a call is by design, so you don't push any buttons on accident and save battery life (since it's on your face, you're probably not using the screen anyway). Like everyone said, you can adjust the behavior with kaisertweak.

Can't help with the sync settings as I only use IMAP and that only allows you to change the sync times so much. YOu could try disabling the email notification sound though (I did) if it bugs you.