Well actually I got the Gas Texture from this pack. [link]
and How to make it into a planet, I Learned a way to Make planets easier. From References,from PSDs.Which made the planets, Seem more realistic in some ways. Compared to the old way I use to make them.
I cut out the Meaty part of the Texture, with the Epilipical Marquee Tool, or how ever you spell it. Placed it on a 2000x2000, Document. Sphereize it. and for the Empty Spots, I try and Clone stamp some of the gas,and Try and Merge it. and As for the Atm. I use a Soft brush, with the color you would see fit, and Placed it on screen. Duplicated once if you want. and as for the shadow, I Made a black, Circle and Did a Gaussian Blur on it.
I do similar things, However doing it this way does not allow you to see the poles of the gas giant (Top and bottom). I find that thats the only problem with that technique, unless your texture is made for it already.