Photoshop :: Specifics On Image Degrading Using Jpegs

Here's a question I never really knew the FULL answer to...

If I take a jpeg image, and save it out as a 100% quality jpeg, does it lose image quality? I always operated (for many, many years) with the assumption that resaving a jpeg degrades the image quality... though I never knew the specifics, like:

1) Does saving as 100% quality save it without adding any image quality loss?

2) Does loading a jpeg (or any other compressed file, for that matter) into photoshop cause quality problems (because the file is already compressed)?

3) Would repeated loading and saving of the same jpeg at 100% quality continually reduce the image quality?

4) Even with an uncompressed image (say, one that you created in photoshop and haven't saved yet), does saving as a 100% jpeg reduce quality, or is it (at that level) like a lossless compression that simply looks for patterns or repeated blocks of the same colour?

5) Up to now, I've always used uncompressed Targas as my 'work image', and only created jpegs from it for emails or final display images (for my portfolio, etc)... with the assumption that as long as I'm going to be modifying it and resaving it, I should use an uncompressed file. Is that being unnecessarily cautious?