Thanks for answering #1, guys. That's basically what I would have said.
2: The short answer is that you kind of can't. You can add several seconds of silence to the end of the BOV sound so that it doesn't loop again for a long time, but that will use lots of file size.
3: Not really sure, but maybe try putting just a little bit of time at the beginning to put a delay? Then again, that doesn't make any sense. Honestly, I just kind of deal with that.
You can make both problems less obvious by changing the RPM range that the sound plays in, but I haven't gotten very good results yet.
Personally, I'd like to figure out how to make a decent turbo spool sound. :/