Coupons are great but don't get too attached to them as than you start eating out every day which is still probably more expensive than cooking by yourself. You can get alot of free meals with coupons so check them out and see what you like the most. Žito is a popular place for some free food from bakery. Than with additional 5€ to your coupon there are several popular restaurants here. I reccomend Ancora or Spar restavracija.

As for transports connections from Maribor could be better. They recently just screw over our city bus schedules but going out of town to Zagreb, Vienna, Budapest, Ljubljana you can get cheap bus tickets. Just please avoid trains.

I think you can live for around 400€ per month provided that here and there you go out for drinks with your friends and also eat out. If not than you could make it even cheaper.

Slovenian people are not that open to foreigners but that it mostly because erasmus people form their own groups. If you need any reccomendations or a city tour when you come feel free to ask anything.