Explanation
The Deutschlandticket is a monthly ticket for all public transport throughout Germany, excluding only express trains. It covers all regional mainline trains and all local public transport. It's a subcription from Deutsche Bahn sold by calendar month. For the group stage, you can thus purchase it at the start of June and cancel it with effect from 30 June (which you must do by 10th June, or your subscription will automatically renew). It costs just €49 a month.

I have assumed that you would travel on your Deutschlandticket or using the 36-hour free regional travel with your match ticket for all train journeys inside Germany except the trip to and from Frankfurt. Using only regional trains for that would take about 4 hours, so I have you 'splashing out' here for point-to-point tickets, which - at an educated guess - I'm assuming will cost no more than €30 each way (that's based on Deutsche Bahn having said that their will be special reduced fare tickets for match ticket holders at the Euros and the fact that for the European Handball Championships in Germany in January the same deal is on offer and the fare each way is €28.90).

The air fare shown is currently (3 Dec, 19:30) available with Ryanair from Stansted. On the assumption that for 13 days you'll need something larger than a small bag that fits under your seat, I've included their £27 charge each way for a bag to go in the overhead locker.

The fares for the bus from Eindhoven airport to the station and from the station to Kaldenkirchen, just over the border into Germany, are as per the bus company and Deutsche Bahn websites.

The accommodation price is as per this listing on Booking.com this evening (3 Dec), based on two people splitting the cost 50:50.

Last trains back
Deutsche Bahn are promising extra trains to and from the host cities during the Euros, but there are no schedules for these available yet. So, I've looked for now at what the last trains would be to get back to Wuppertal after the games in Gelsenkirchen, Frankfurt and Cologne as the timetables currently stand.

After the Gelsenkirchen game: This one could be cutting it fine to catch a train for which your matchday ticket or Deutschlandticket is valid. As the kick-off is at 21:00, the game is likely to finish between 22:45 and 23:00. If you got back to the station quickly, there's a service showing on the current schedule for a Sunday evening at 23:54, getting you into Wuppertal at 01:08. Failing that (and in the absence of any extra trains being put on), there's a service at 00:44 that gets you into Wuppertal at 02:02. However, the first leg of that journey is on an ICE (InterCity Express), the normal fare for which is €17.90.

After the Frankfurt game: Kick-off is 18:00, so the game should end between 19:45 and 20:00. From the airport there are trains up until 22:21 on the current schedule (arriving in Wuppertal at 00:36) and from the main station up until 21:47 (00:36 into Wuppertal). 

After the Cologne game: Kick-off is 21:00. So, like the Gelsenkirchen game, it should end between 22:45 and 23:00. There are direct trains from Cologne main station at 23:52 and 00:52 (the latter getting to Wuppertal at 01:36).