Turning off digests is possible, there is a disable email summary setting.
As for the rest, those are user preferences, You can select defaults but I am not sure if this will prevent users from changing that to something else.
As far as I can tell from current core, category moderators receive the on-site review notification for flags in categories they moderate, but they don’t receive the delayed system PM/email reminder simply by being category moderators.
The PendingReviewablesReminder job sends that reminder to the moderators group, and the users it explicitly mentions are selected with User.where(moderator: true), i.e. full moderators. [1]
So a category moderator who is also a full moderator would receive it, but category-moderator status on its own doesn’t appear to make them a recipient.
Also, hiding the normal email-preference controls with a theme component wouldn’t change this, since the moderation reminder targeting is handled separately on the server side.
Okay well maybe not so important for non full staff to receive those email notifications then as many in that category would already likely be fairly regular.
As most ppl these days are quite active in sites. I am aiming to reduce email output to a minimum.
Still need to look into it more but thinking RSS Readers could be a good fit instead of email as content would not require time sensitive quick responses for the most part