That is correct - all the tapes in a spanned set must be inventoried and cataloged before a restore will work properly
As for the speed, it is my experience that restores run about a factor of 10 slower than backups do. I've never seen it mentioned in any documentation from Seagate/Veritas/Symantec, but it has been liek that since v7.0 So if you backups take about an hour per tape, restores will take about 10 hours per.