I'm going to stay at Leo Hostel at 52 Dashilan W St, Xicheng Qu, Beijing .

Yes, the surrounding transportation is convenient.
From your hotel, you can walk northeast around 900 meters to Qianmen Station. Take metro line 2 to Jishuitan Station. Walk to Deshengmen Bus Stop, you will easily find the bus no.877 to Badaling Great Wall.
If you wanna visit Mutianyu Great Wall, you can also take subway line 2 to Dongzhimen Station. you can take bus line 916 Express to Huairou North Avenue. Then, transfer to bus line h23, h24, h35, or h36 to Mutianyu Roundabout. Afterwards, walk 450 meters to the ticket office of the scenic area.