Regarding question 1: There’s currently no way to remove this text completely. However, you can change this to be a “More information” link that links directly to your Octopus Server’s audit screen. To do this, please see the “Email Notifications” section of the Subscriptions documentation, where it discusses “Emails may also include a link to your Octopus Audit screen”.
Regarding question 2: Unfortunately we don’t expose a template for digest emails. If this is something you’d be interested in, you could raise a Uservoice suggestion and if it gets enough votes we would look into adding this as a feature. As a workaround, you could write an application that your Octopus webhook subscription could send events to, and send customised emails from there. We did a recent blog post showing a simple Slack notification that may be of interest.