Display & Keyboard Sync
The latter half of your question, adjusting keyboard backlight from ambient light, can be achieved in System Preferences → Keyboard → Adjust keyboard brightness in low light.

This won't adjust the backlight if you manually adjust the screen brightness. If you don't use the ambient light sensor for the display, you can use some hook on the increase/decrease brightness keys to also press the backlight brightness keys at the same time, using an app such as Keyboard Maestro. Otherwise, you can use Keyboard Maestro with some loop to get the display brightness on regular intervals and set the backlight brightness appropriately.