I think your main data usage culprits are the apps. I know with UberTwitter there's a setting where you specify how often you want the app to refresh and look for new tweets. You might try to lengthen the intervals at which it does this.
Aside from that I can't think of any settings within the BlackBerry itself that would help too much with keeping data volume low. Because they are apps, any control measures would be something adjusted in the app itself and not your BB device.