If you go into settings and begin the process to reset the tablet, you will have the option to securely erase the tablet. That'll be all you'll need unless you need some REALLY secure. Like disk destruction level of security. And if you do, you probably have an IT department to take care of that for you already.
Bitlocker is the name for Microsoft's full disk encryption. It doesn't hurt to enable. It'll just take some time to encrypt the entire disk. I wouldn't worry about it now if you're erasing it though. Maybe as an extra measure, but the secure erase reset thing should be good enough for most individuals.