Katarina's apartment was great. It was more than large enough for my three person group, and had good amenities. The location is great, close enough to grocery stores and a small market, not to mention just a small walk to Brandenburg Tor and the Unter den Linden boulevard.
We turned in our rental car at the start of our Berlin stay, and there is economical parking that can be arranged if you need it. However, I would honestly ditch the rental car when in Berlin entirely, rent a bike at the corner market, and walk/ride everywhere you want to go. It's a 13 minute ride to the Berlin Wall Memorial, 10 to Museum Insel, and almost all the roads in this part of town are easy to navigate via Bike - even for those of us who haven't ridden a bike in a long time! :)
Katarina was a perfect communicator. Fully explaining the check in/out process, parking availability, and quickly answering any questions I had. She is truly a great host.
I would absolutely stay here again, given the chance.