I have V5 editor, upgraded from V4 assistant. I also use reaper.

The editor version with the ability to tune chords is brilliant! I've used it to change chord voicings in realtracks, and also to tune my own rhythm guitar tracks to compensate for intonation issues.

Another thing I've used it for a couple of times is to change the feel of a realtrack bass part from swing to straight.

One of the great new features with V5 is the sibilance balance tool, works better than any de-esser I have ever tried.

Dan answered all your questions except for 2, which I also don't know the answer to, I never tune to a scale.

But, I think they offer a fully functional demo, why not try it and see if it works for you?