Does stress increase or decrease metabollic rate?

No difference likely. Stress shouldn't have a significant effect on metabolic rate either way, but it can increase cortisol levels which can cause weight gain or make it more difficult to lose weight.
Doubtful effect. Stress causes release of hormones which do not effect the metabolism as much as they effect the heart, blood pressure and emotions. It may effect metabolism in subtle ways by interfering with sleep which then leads to other metabolic changes effecting appetite and lead to weight gain.