What are details of order of execution among validation rules, auto-response rules,
assignment rules, triggers, escalation rules, workflow rules etc.?

Answer: See the explanation.

Explanation:
1. System validation rules are executed like data type checking of the field values. So error for text value in numeric
field etc.
2. Before triggers execute.
3. Custom validation rules are executed like required field check validation rule. So in the before trigger you can assign value to any such field which was left blank while creating the record & the custom validation rule won’t give error then.