Lossless Linking and different media formats


I am archiving data to DVD-R media using UDF version 2.5. The writing software is native Win 7 OS. I usually do multi-session recording. (Without closing the sessions) I have re-read Scott Mueller’s chapter on Optical Drives (in Upgrading and Repairing PC’s) several times, but am still confused on several things. First, am I wasting space on the DVD between sessions? Second, does true “lossless linking” require a re-writable media such as DVD-RW or DVD+RW…perhaps due to erasure or modification of lead-in or lead-out information? Third, does DVD+R media support lossless linking?
Finally, can a formatted read only DVD be ruined by accidentally trying to reformat it again? Windows gives me a “format” option when I put in a partly recorded disc…Hope these questions aren’t too boneheaded… Peter