Chris,

*Suggestion 1:* consider making _all_ Group Notifications
*un*moderated, ... hitherto File uploads have been “instantly”
notified. i.e. unmoderated.

On 2020-06-19 these were put under control of the group's Message Moderation setting, as not doing so was seen as a bug.
https://beta.groups.io/g/main/message/25466

I think it also served to avoid forcing group mods to find/create each relevant hashtag and mark it "Moderated". At least in moderated groups.

Where an individual member chooses to notify the membership of an
upload the existing configuration sends Moderators (a) a Moderat*or*
Notification, (b) a Moderat*ion* Notification (subject to Group
Moderation Setting – see above) and (c) the “published” message,
i.e. 2 or perhaps 3 related notifications.

In addition, (a) and (b) are visually almost identical,

Your (b) has the Subject text "Message Approval Needed ...", making it quite distinct from the other two, IMO. And the body content is completely different.

and their arrival in order (a)(b) is not certain. ... This is likely
to be a source of confusion.

Why? I guess because you think they're visually almost identical, but I'm not seeing that in either the Subject or the body text.

On the other hand, (a) and (c) have /similar/ subjects and bodies.

But (a) lacks the hashtag in its subject, and has your email address in the To: field, whereas (c) is hashtagged and has the group's posting address in the To: field. Their footers are also different, with (c) having the standard group message footer.

*Suggestion 2:* When a member chooses to Notify members then the
Moderat*ors’* Notification is superfluous and should not be sent.

It isn't though. At least not for a moderator who doesn't have the permission to moderate messages, or who has turned Pending Messages notification off.

*Suggestion 3:* (a) and (b) need to be /much/ more easily
distinguished,

See above.

*Suggestion 4:* either ... or change the Notification “subject” so
that it applies to “changes” rather than being specific to deletions
or uploads.

I vote for that one. At least when aggregated.

I assume that the “aggregation window” opens when the first deletion /
upload / edit is triggered.

Correct.

Does a second related “event” reset the timer so that the window
closes after x minutes of *in*activity or is a fixed period after the
first action?

There is a single reset of the timer. So after a max of 2 x 4 minutes.
https://beta.groups.io/g/main/message/25552

Shal