Can I see who opened an email attachment, or get an alert when someone clicks a link in my email?

There is no way to tell who opens an attachment. If you want to know, send a link to the file instead of attaching it.

For alerts, use the Email link clicked trigger to start a workflow that sends you an SMS or a push notification, so you can call the person. With many emails this can produce a lot of alerts.

Another option is automatic lead scoring under Settings, General. It scores contacts on all their activity, such as opens and clicks, so you can sort contacts by lead score, filter for people above a certain score, and use that in a workflow, as a call list, or to notify yourself.