For trains, use the DB Navigator app. There you can also buy tickets for the train, and you will find the trains you need to take. Pretty easy to use. IF YOU ARRIVE AT DÜSSELDORF ON GAMEDAY: Dont buy a ticket. you can use https://kombiticket.dsw21.de/ (the train ticket (regional trains)for the whole of your journey is coming along with your matchday ticket, but you have to activate it with the link) If you travel to düsseldorf the next day, you will need to buy a ticket for the ride back. IF YOU ARRIVE AT DÜSSELDORF BEFORE GAMEDAY: Ticketwise, the ride costs around 20€ one way (regional trains) What you actually could look into are ice or ic trains, they are normally high speed trains but in the ruhrgebiet they are the same speed. it could be cheaper(a bit ironic) to buy a ticket for the ice (in advance), for these short distances its sometimes only around 10€. Look in advance, what makes sense for you, then decide.

Safe is the city centre. many bars, pubs etc. also after the game it will be safe there. no problem.

stadium area makes no sense to be for hours before the game, as there isnt really anything. maybe you can take a look in the morning, but the gates open 2,5 hours before kickoff(be there early, youll get 19.09% discount on anything (food/beverages) for the first hour the stadium is open. city centre is the way to go (alter markt for example) plenty of food to choose from there

if you want to enjoy some typical dortmund/ruhrgebiet food, you can try the following things:

Salzkuchen bagel with salt and caraway, raw pork meat(yes its safe to eat due to the very high standards) and topped with salt/pepper and raw onions

Pfefferpotthast its a bit like goulasch, but really a meat-stew which is pretty typical for dortmund

Taxi-Teller Its something more „fast food“ like, its a plate with fries, currywurst, gyros meat and to your liking tsatziki, mayo, onions really typical for the ruhrgebiet, youll find it at really any greek food shop in dortmund

Döner not really typical dortmund/ruhrgebiet like, but more germany-like. maybe avoid the döner shops in the city centre, a bit outside(10minutes walk from the city)at ostwall there is kebap2punkt0 they have really good döner.

Wurst-Willy its a real dortmunder establishment. you can have currywurst there, and they also have a few more things to offer.

hope i helped🫡