I Have a way of making clouds, but, its complicated and eats up rendertime:
If you have ever read the tut for “fur” back in the day, then this would be easier to explain. Try making a sphere that has many layers, something akin to, say, a baseball, just with alot more layers (at least 9) with very little space in between. Now, give it a texture (try cloud for starters) and make sure it starts at alpha 0 (from the left hand side) and goes to alpha 1 (or less, if desired). Now, make your sphere material ztrans, and all shadow options turned off to see where the general layout is. Change your ramp sliders to where you wish, or the noise size/depth, or even the mapping size. When that look suits you, turn on all shadowing options (even bias if you are using ray) and voila:
Notes: Won’t work right with reflections or refractions, and shadows may look…odd at certain points.
Now, the sun part is easier - layer halo points:
I did this with 4 points, 1 with your general halo with hardness all the way up, alpha 0.5, add 1.0; another with your general halo, hardness all the way up, alpha 1.0, add 1.0, and about half the size of the first; another with the star option, hardness all the way up, alpha 1.0, add 1.0, and a little bit bigger than the second point but smaller than the first; and lastly was a halo with the lines option enabled, hardness all the way up, etc., and about the same size as your “star” halo.
Notes: Pretty much the same as above.
Hope this helps