JPGs use lossy compression so some pixels aren’t exactly the same anymore; however, if you use the highest or close to highest quality setting in LR during Export it will be hard to tell any difference.
JPGs are compressed by contain 3 colors per pixel whereas raw files (NEFs in your case) usually contain only one bit per pixel and are compressed in a way that makes them smaller but doesn’t lose any image data.
TIFs if not compressed are the width x height x 1 or 2 bytes per pixel x 3 colors-per-pixel so can be huge as you have seen.
If you shoot JPG and edit those in LR you still cannot see the LR edits in those original JPGs, only the camera rendering.