Tourist Bus Line 1: Qianmen ⇔ Badaling

Hi,
We are intending to catch this bus - we are staying at -
The Imperial Mansion, Beijing Marriott Executive Apartments, North Gate, No. 1 Xiagongfu Street
Dongcheng District and have the following questions:

1. Is the bus center walk-able distance? We are intending on travelling on Wednesday 26th July and wondering what is the easiest way to get there. There will be 3 adults and a 2.5 year old.
2. How do I identify the tourist bus?
3. Can you prepay the great wall entry tickets and return trip on same bus at the start of the day at the bus center?

All help will greatly appreciated. Thank you