mystimoods has a lite-c conversion and features both things: http://www.loopix-project.com/

shortly:

1) you can tweak sun_angle.pan and .tilt to set Sun position (a short time ago there was a contribution that sets it perfectly), sun_color to set a proper color, and sun_light to decrease sun_color brightness.

2) see TUST for effects, or mystimoods again

3) probably you need a blueish fog. if you can use shaders you can take the caustic shader from mystimoods simulating underwater lights, and maybe a refraction post process shader to distort the view a bit