WOW! - that is quite a few tasks and would take some time to put to gether - would be quicker to install NOM - although 6.5 will end support in October so you should be looking to upgrade and use OpsCenter.
Quick ideas as a basis for you:
1) pipe the du command for each client (/netbackup/db/images/clientname/) to a file and then script it to see what the difference is from the previosu day - or similar?
2) bpimagelist -client clientname -L (or -U) -hoursago 24 and grep the kilobytes (or KB) figures - again pipe somewhere to then compare with the previosu day
3) bperror -U -client clientname -hoursago 24 and gerp this for the Kbytes/s figure - will also provide the figure for 2) above
4) bpimagelist -U -media -hoursago 24
5) bpimagelist -U -hoursago 24 to show all images or use the df / du commands
Not much help but I hope it gives you some ideas
