"1. Removed disk from disk group 1 - Full data evacuation (What would the difference have been if I chose ensure accessibility?)."
With EA(Ensure Accessibility) option it would wait for the clom repair delay timer (60 minutes default) to exceed before recreating the 2nd replica of data that resided on this disk - with FDM(Full Data Migration) it recreates replicas before removing the data on the device you are removing.
"1. Do I need to clean the disk first? If so should this be done at RAID level or vSAN (Storage Adaptors - Erase Partitions on the Selected disks)"
If the device was successfully removed then it should have no partitions on it - this can be verified in a number of ways including looking at it directly in /dev/disks/ , via Web Client Host > Storage Devices > Select device > Partitions or by seeing is it available to add to an existing Disk-Group: Cluster > Manage > vSAN > Disk Management > Select Disk-Group > '+' disk icon
If these devices are/were individual RAID0 VDs per device as opposed to passthrough, you shouldn't need to reconfigure this.
"2. Do I need to "claim" the disk or "add a disk to the selected disk group"? (What is the difference?)"
Not sure if you are referring to autoclaim or what, just add it to the Disk-Group with less devices.
"3. Once the disk is back in the group, will vSAN start moving objects onto it or is it recommended to do a manual disk re-balance?"
No, by design it won't start moving stuff unless any devices are over 80% (default) and can move data here within compliance of the Storage Policy applied to the data - use manual rebalance via the GUI or RVC (where there are extra options) to initiate moving some data here immediately.
Thank you for a rapid detailed response. Massively appreciated and meant I could confidently complete my maintenance over the festive period!
More than happy to help.
Though to you and anyone else reading this: if you have VMware/other support for vSAN, please don't be shy with logging a Support Request with us - even if it just for clarification or something you think is relatively trivial - we do not bite and prefer proactive guidance/clarification over fixing something broken as a result of improper procedure so you may actually be doing us a favour .