1. Sync your old BB to Outlook or Google and sync the new one to the same. That will transfer contacts and calendar. Or use the Switch device wizard in Desktop Manager.
2. I do not personally know of a pay-as-you-go BB plan especially if you also want data. If the device is unlocked, you could get any voice pay-as-you-go SIM as there are several out there.
To return to factory settings / or to remove the old data, do a security wipe. BlackBerry 6 Security: How to Wipe Your RIM Smartphone, Restore Factory Settings CIO.com