I think you already received your answers and seem satisfied with them.
SiteLock is an offering from www [dot] sitelock [dot] com which really ends up being an image you get from them to put on your website that gives your viewers a bit of comfort because at the end of the day, Bluehost manages their servers and ensures the security of the servers so you don't really need this service.
Site Backup is unecessary because in the control panel, you can download a backup anytime you want directly from the server. I guess if you don't trust yourself to download a backup routinely then it might be worth the cost.
And domain privacy as explained above by other members is so that your Name, Address, Phone Number, and Email address are not publicly displayed but you only need to purchase this from them if they will be your domain registrar.