Accommodation: Baxpax Downtown Hostel - we decided to start with our go-to accommodation - hostels, but we switched it up a bit this time. We found a hostel/hotel that had private, apartment-style rooms for a reasonable price. A room with three beds and a private bath (and kitchenette) cost us $30 each/night (the same as my bed in a 12 person mixed dorm room in Copenhagen). Since we came at low-season/during the week, we seemed to be the only adults surrounded by a group of rowdy Spanish teenagers on a school trip, but I could see it being great during the main tourist season/weekends. It was in a great location right next to the metro station.
Transportation: We would definitely recommend investing in a multi-day travel pass for all 3 zones. We didn’t realize how spread out Berlin is until we arrived, but it’s honestly much easier to get around by metro (especially in March when the weather is a bit chilly and rainy). This card lets you travel to any zone for free. Just make sure you validate it and keep it on you as there are sporadic checks by workers.