Not really in answer to any of your specific questions but here's some thoughts, in no particular order:
The lions share of that task will be ensuring that all those who must be notified/consulted are served a copy of the new tpo's and notified when an old one is revoked. If you have an admin team available who will prepare lists of addresses and land reg for owners, then print off all the necessary papers, stuff the envelopes and serve them correctly then that's fine. Do not underestimate how many people you need to notify but don't let that be a reason to not review your tpo's.
I'd start with your area tpo's, generally working from the oldest to the newest. The exception to this might be with relatively recent area tpo's on large, incomplete development sites but where you are able to accurately map trees so they don't end up plotted in the middle of roads (say, if you manually plot them and don't have very good reference points to map them from). The reason for this is that you can significantly reduce the number of owners/occupiers you need to serve to. Once that is done, the tpo will show up on land searches so the solicitors can do the legwork for their customers. Once the land is divided up into individually-owned plots, this task becomes more burdensome for you.
Use your planning system to sift through old tpo's and applications. Back up using Google maps, bing maps and Google streetview. Look for trees which have been felled. Work out what was supposed to be replaced (by condition) . Make a note of unconditional fells, check they were felled, revoke the tpo's if all trees on them felled. 'The Silver Birch at Post-War Household Tree Preservation Order, 1953' is unlikely to still be there and I bet they didn't comply with the condition to replant in 1967 either.
If you have one, train your admin team to sift through all of your original tpo's and check all of the essential components are there. Pages go missing over time. Look for incomplete tpo's (e.g. no evidence of confirmation, no site plans) and put those to one side. Check the details and see if the pages turn up in another folder. Consider resurveying and/or revoking.
Get digitised if you haven't done already. If you have online mapping through your council, you should be able to link scanned copies for download directly off the map.
There's loads of other important things to do but this is just a few thoughts from recent experiences.