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In the scenario you present, your LR edits are made non-destructively to the TIFF file, not the raw.
Different people like different work flows but in general I would recommend trying to get at least your basic exposure and white balance set in the original raw before the edit in Photoshop. If you know you will be going to PS anyway, most of the other things (healing, dodging, burning, HSL adjustments, etc.) you can defer to PS if you want. It really depends on which software you find does the best job with the least amount of effort. You might want to consider doing a little noise reduction and capture sharpening in LR before the move to PS - again, there is a lot of personal preference involved and it depends somewhat on the characteristics of the specific image (how much noise, for example).
If you want to give yourself a little more wiggle room at the expense of larger file sizes, you can bring the image from LR into PS as a Smart Object. This allows you to open up the Smart Object and re-adjust your original raw edits. How helpful this will be depends on the types of edits you are doing in PS. If all your PS edits are standard adjustment layers it works pretty well. If you are doing a lot of cloning and healing or like to use intermediate "snapshot" copy layers, it works less well since those things will probably need to be re-done if you change the Smart Object.
As long as you are bringing the image into PS as 16-bit, the loss from raw is not great UNLESS you make radical exposure changes after the image is in PS. The raw file contains anywhere from 12 to 16 bit data, depending on the camera, so it sounds initially like a 16-bit TIFF or PSD would work fine without any data loss. The problem is that the tonal values are not distributed the same across those bits in the raw as they are in an RGB format like TIFF or PSD, so tonal values can be lost (primarily in the highlight values) in the move from Lr to PS. This is why it's a good idea to make your basic exposure adjustments (including possibly the LR tone curve) before the move to PS.
Now with all that said, it may or may not be necessary for you to worry about these things. It depends quite a bit on how much you are going to enlarge the image and just how anal you are about image quality.