[Five]

if you burn with verify enabled and it comes out okay, it should be perfect. you can double-check by generating md5 checksums from the DVD you burned and also from the DVD you copied. They should be exactly identical. It is a little bit different for audio cdrs, but applies to FLAC "data" discs equally.

Burning at a slower speed makes for better longevity (so its been said, not exactly proven but I do believe this).

I have never had a problem with sharpies, been writing on lots of discs for years. If you're trading its good etiquette not to write on the discs or attatch post-it notes directly to the disc.