Beijing Forbidden & Beihai info

Hi-3 of us will visit Beijing next Tues. We will spend 3 days on our own before our guided tour. We like to spend time at the Forbidden City, Beihai Park in 1 day. Then visit Hutong, Bell & Drum tower in the evening.
Is It cheaper to get a 1 or 2 day subway/bus pass? $$$? How far walking from Palace to Beihai?
Thanks