Higher FPS = reduced latency
On my system it builds the buffers only once. Not every time it's launched like you say.2) That's not true - R12 pre-buffers the GUI every time it's launched so after the project's loaded first time it lags a lot until everyting is buffered
The frame rate and the screen refresh rate are different. It's highly unlikely that S1 is animating UI elements at 144 fps.3) Many DAWs will refresh the GUI as fast as your GPU and screen allow, so e.g. Studio One runs at 144fps here