This may not be that helpful for your specific questions (I didn't check them), but ..
It is so much easier to go with plain, standard, unmodified etc cars if you're hotlapping; others shouldn't then have any problems following your drive. If you want to show off some nice cars/skins, then Fraps-to-AVI path is probably a better way.
Remember that anything (graphical) that has changed won't show up when replaying the file *without* that exactly same modifications (so why use??). If you were to use so-called standalone car (with a new *.CAR file) for some new skins there's a possibility that replayer won't see any car at all (invisible) or some random other car with weird sounds. Also standalones adds a risk of other updates that might change the original car performance (which may not be clearly pointed out in readmes).
For the above problems there have been set some rules, making people remember and obey them is another thing .. : /
cheers.. aSa C[_]