General questions about synchronisation

[C Psyctc]

As per my previous post (Restoring copyq config from a backup of ~/.config/copyq (Linux)), I am back to thinking about synchronisation across machines.  In the past I remember I tried setting it up to synch between my main Linux machine and CopyQ running in Windows (10) in a VirtualBox VM but I think abandoned it when I realised that mostly I only really needed the automatic copy buffer sharing that VirtualBox provided, on top of exporting the whole tab structure from the main machine to the VM from time to time.  Given the havoc losing my main machine (despite having onsite and offsite backups), I am keen to have more things synching across four machines: main Linux machine, older fall back Linux machine and a little, slow, travel Windows machine ... and the Windows VM inside the main Linux machine).   All machines will be linked to my NextCloud account so have a directory that synchs pretty quickly.  My tab structure changes only rarely and additions will only be from the main Linux machine so my questions are:

1. I seem to have some broken Syncronisations, i.e. tabs with no file link, left from earlier, is there a way to deleted these?  Does just deleting the tab name and making sure there is no file map to them empty them safely?
2. I suppose there is some occasional utility to having the clipboard tab itself synched across those machines so is it likely to be OK, as per using DropBox (ugh), to just map that tab to a file in the Nextcloud folder in each machine?
3. It's not easy to set up synchronisation on all tabs so I'm not going that way (not least as I have a lot of tabs and it would take me at least an hour I think to set them all up).  I am guessing that not making it easy to synch a lot of tabs is a sensible design decision to prevent creating a lot of separate files and a lot of synching traffic that, at least for me,  I don't really need.
4. I will use the "Backup On Exit" command on the main machine (but not the others) and try to remember weekly to import the latest backup from that to the other machine so their tab structure and contents are rarely much out of date.  It seems to me that saves a lot of really unnecessary traffic through NextCloud and work for the CopyQ programs while preserving what I need.  Any obvious counterarguments.  Is there a way to synch all tabs and keep all synched?  Or am I correct about the reasons for not doing that?
   

Sorry, long question but I hope it thinking, and any answers, will be useful to others as well as to me.

TIA,

Chris