The apartment is absolutely beautiful and the perfect space for a big group of friends. It's nice and roomy so you don't feel on top of each other and the large dining table is the perfect place for a few card games/evening meals together (plus the beds are super comfortable!). Equally, Dlauer makes it seem like nothing would be too much trouble and is very speedy to respond, making communication an ease.
The other great thing about the apartment is that is has such amazing public transport links that it made exploring the wider areas around Berlin really easy. It's also got great amenities close by so a morning stop in the coffee shop just on the corner from the apartment gives you the opportunity to try some delicious pastries. If you want some tasty meals then the restaurants around the apartment are fab and for some interesting cocktails you should head to Salut! which is about an 8 minute walk from the apartment.
If you're looking to find out a bit about the history side of Berlin then head to the Brandenburg Gate and go on one of the free walking tours. They take about 2 and 1/2 hours but it's incredible and it also means you get to see other places to visit. If you're after art and culture then book the Alternative Tour that takes you to the great street art spots and the East Side Gallery. The spy museum is also a must!