You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
Back will be dark grey with the logo on top but I am just not sure which would be better for the front.
If you already have a background colour on one site, stick to that. One side grey and one side orange sounds very "noisy". Without knowing what exactly the two colours are, I think I would go for the orange, as it gives you a pop of colour, but also allows for notes on the card.
The hexadecimal color codes would be: e27c00 - Orange 2f2f2f - Dark Grey As an example, see the attached image. This would, more or less be how the back would look, only with a more up-to-date logo.pic.twitter.com/Ycs7psV3Ot
Could work, but you'll have to be careful with font size and amount of text as to not induce eye cancer. With your back, I'd personally probably go for something similar to this for the front:pic.twitter.com/cEShfUytV1
I'll see about mocking something up later. Would you go with the orange rather than the grey for that color pop and easier writing/reading?
Yes. And I feel the switched colours from back to front give the card some extra dynamic in addition to the colour pop. I would also print out a bunch of different versions to see what feels "right" to your eyes.
Im afraid test prints wouldnt allow me to hold a finished product in hand before Gamescom x:
Doesn't have to be with the printer, print them out at home. Even a low-quality print gives a better impression of the finished card than having it on screen only.
Here's hope my printer cooperates. 
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.
