The maximum split size is 2048, and is also the default split size when saving to network drives. You can therefore save two GHS files per single sided DVD and four per double sided DVD. The figure 2048 was the maximum file size that could definitely be saved on a network share regardless of whether the share was NTFS or FAT, and dates back to early NT days. Ghost **should** be intelligent enough to work its way through both or all four GHO/GHS files before asking for change of media.
One thing I would strongly recommend, and that is to archive the source files on a GOOD QUALITY portable hard disk or a server share, as optical media does not always last well. Buying a recognised make is definitely worth the extra $, as I have seen visible "holes" in the media surface of cheap disks. You might be able to get away with it on audio or video content, but data will definitely barf on read sooner or later where there are defects. Likewise cheap USB drives can have a higher soft error rate than WD or Seagate drives (for example).