a) I guess it might depend on your settings, but really, if it is DV material then that does seem rather long. Are you SURE you are not selecting Quicktime Compression and not Quicktime Movie?
b) It makes no difference. That is really for exporting back to tape.
c) See answer to A.
d) DVDs ONLY use MPEG-2 compression. If you compress to MPEG-1, then try to use iDVD, it will recompress that to mpeg-2, making your picture look really bad.
If you use iDVD, export as a Quicktime Movie…self contained, sequence settings. Then inport that directly into iDVD. Pay no heed to the file size at this point…iDVD will compress it. Unless your movie is over 2 hours, then there will be issues.
If you are using DVD SP, then take that exported quicktime movie and use Compressor to compress it for you. There are easy to use presets.
I have no experience compressing mpeg-1 or mpeg-2. I only use iDVD when I need to. Most of the time I go out to tape.