I can't see any reason why you shouldn't be able to use Gmail Calendar without MS Outlook. If you to go mobile.google.com from your device you should be able to setup the Calendar from there.
If you do want to import your Google Calendar items into MS Outlook, the BlackBerry will not remove any data from that computer.
I don't know about transfer speeds for the different carriers. I use Sprint and a BES and can usually get my emails within 3 minutes of being sent.