I've been to this place and photographed there.
No problem with 400 handholding. Tripod or other support is never a bad idea, though, but making photographs there was pretty easy. As always, be respectful -- this is a place extremely important not just to the Chinese people but humanity as a whole, too.
Lighting conditions do change, depending on time of day, cloud cover and weather, etc. But no problems, as I said. You may want to take either a spot meter or various readings, as highlights play among the vast crowds of figures...you could meter for shadows and end up blowing out the many highlights.
When I went there, it was at the plans of my former (Chinese) professor. I wasn't keen on going as I wanted to try avoid overtly touristy places...I'm so glad he did plan for us to go there, as I was just blown away.
I'm not one to be overly sentimental or prone to that sort of thing...but as I said, it was a very moving and powerful visit. A real wonder of the world. Enjoy!