Hi Wil,
A) If you do not check “Recompress all” only are recompressed the clips in wich you have change something (effects, motion tab,..) If you only set IN-OUT and export USING QT (NO QT CONVERTION) you are just exporting a piece of the original footage. Not loose of quality at all. The same is if you export a refference movie.
B) Export with a different codec would be interesting for you if you would pre-process the clip in FC. For example if you would apply a kind of Chroma Smoothing to make easier to pull the key, you should export the clip as 8/10b Unc or so. If you make this pre=procesing in FC and them you export as DV the pre-procesing would be waisted.
C) I always capture DV. It take less space on the disks and in case any capture-card would introduce any improvement in the image, such a improvement can be done through software too.
Cheers,
rafael