I mainly lurk, and that not too well, so please excuse me if this has
already been raised under this thread.

Who are the 2 or 3 taken along in verse 16 and, especially, to what are they
witnesses?

I have generally heard them described as witnesses to the confrontation
between accuser and accused. Doesn't the reference to Dt.19:15 (and paralel
instruction regarding elders in 1Tim.5:19) rather suggest that they should
be witnesses to the alleged offence?

David.