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.