Thanks for the posts above, it helped immensely (even though I am still learning [slowly] so a lot of it is over my head).
I installed a New copy of TES and all of the CC content, cleaned the "dirty" plugins with SSEEdit, (strange how all the dirty ones were from "official" CC and Bethesda) which left very few loading reports in Papyrus.
The original "Battle-born Farm" problem was caused by "Valkyrja Castle" mod (thanks Leonardo) and the Weaponsrack errors were caused by "Valkyrja Manor" mod (Thanks Arthmoor) - Both mods consigned to the Do Not Use folder.
It appears that the original "callback" issue is actually a MS Windows function and therefore nothing that Papyrus can get around but it still reports it but doesn't seem to affect game saves.
The errors reporting about OBIS and Prettier Bandits was easily resolved by actually installing both mods and simply ignoring them in-game so the Papyrus log now look a lot neater and my OCD is satisfied.
For me "good practice" means using Loot AND running FNIS when installing/uninstalling any mod, and even when starting a new session. I also found it helpful to delete the "meshes" folder from FNIS outputs when visual glitches occur at the start of a game. Once I have a stable Load Order then I use racemenu to create a few named character profiles and save each one for any further testing of mod set-ups (i.e. trying out "Bruma" or "Legend of the Dragonborn" and since I am using MO2 this keeps my vanilla Game reasonably "clean"). Thanks for all the advice my friends. Kudos to all.