I seems like Kevin has done a greg job of answering your questions. I have a couple of other points that might be helpful to you...
First of all, don't be confused by Lightroom's "Back-up" feature in the Catalog Settings. It backs up your Catalog only, not your original image files. Furthermore, it only backs up your Catalog to the same hard drive - a bit useless if you are trying to protect yourself from a hard drive failure! Remember, the Catalog has your metadata, a preview and your Develop/Print/Web and Slideshow settings for each image and Collection but it does not have your original image files.
If you are already backing up your hard drive on a regular basis, then there is no real need to back-up the LR Catalog separately.
I have found it helpful to keep all my original image files in a folder called LRPhotoLibrary. I advocate doing this so that photos don't just get dumped into "My Pictures" - it keeps things "tidy". You most likely already have a file structure that works for you, but if not, this is what I do... Within that LRPhotoLibrary folder I have sub-folders for each year: 2011, 2010, etc. Within each Year folder are the image folders for each shoot based on date: YYYYMMDD-DescriptiveFileName. While Lightroom does an excellent job of keeping track of the location of files, every once in a while one goes astray which I can easily find because of the file structure I've set up. At the same time, once your Catalog is built within Lightroom, it is important to remember to move files and folders from within Lightroom so that it will keep track of the changes.
Since you already have your originals on a hard drive, when you commit to creating your Lightroom Catalog via "Import", you will be "Add" them to Lightroom, not "Copy". Choosing "Add" does not move the photos, but references them to their present location. Your TB of photos will take a long time to import; you might consider doing a year at a time.
When importing, you have the option of specifying what size of Previews Lightroom will create for each image and store in the Catalog (see Catalog Settings > File handling). I would recommend something smaller than the 2048 pixel maximum. When you need it, Lightroom automatically creates a 1:1 preview (e.g. for looking at details, sharpening, etc.).
Good luck with this and don't hesitate to ask more questions!