Send mail notification when node of given type gets created
Answering the "what do I put in the 'type' box?" question, the answer appears to be the same as for D7 - that is, the same status you'd pass to drupal_set_message().

This gives you options of:


status
warning
error


As to the state of D8 and specifically D8 rules, I share your pain - and it's nine months since you asked the question!