You can visit the Great Wall on one of the tourist buses to Badaling. Just do some googling and it will show you how/where to meet the bus. That said, I don't recommend that. It feels like a cattle call, the bus stops a jade shop, Badaling is overrun with tourists, etc. I'd recommend getting a car a driver to another part of the wall that is less crowded.

Temple of Heaven and Forbidden City are very straightforward to do on your own. Note that taxis outside the temple of heaven will demand about 5-10X the going rate. Use the Didi app to get around.