VizAlerts doesn't have the ability, unfortunately, to trigger off of multiple sheets in a dashboard. See Dashboard with Hidden Embedded Alert in the user guide. It explains that to designate the one sheet in your dashboard you want to use as an alert, you must make sure the name of the sheet comes first alphabetically among the others. Typically it's easiest to just put a hyphen or something in front, e.g. "-MySheet".
But as that likely won't get you everything you want, which is multiple alert criteria...here is another option. Create new, very simple sheets that aren't part of your dashboard, and make them your "trigger views" for the different alerts conditions you want the email sent on. Set each of these up as their own alert, and for the email body, use the VIZ_IMAGE() content reference to embed the image of the full, 100-sheet dashboard into it. Now when any of the trigger views goes off, it'll email the full dashboard. If you can consolidate any of the trigger views into a single one, it's better for both maintainability and you won't have as much likelihood that two going off at the same time will generate duplicate emails.
Finally, make sure that the Email Action is added to the sheet, or sheets, you want to alert based off of. If it's defined, but only left over on the Dimensions / Measures pane, it won't be recognized. It has to be part of your viz in some way, shape or form. If you don't want it showing visually, add it to the Detail shelf.