Hi denis, welcome to the forum
I've working in my own similar project of a planet in terragen, you can see my thread here:
http://www.planetside.co.uk/forums/index.php/topic,19476.0.htmlWell, is the earth indeed, but many similar concepts are applicable here. for example: for my oceans I used the solution that Dune suggested you, and works.
I used a global DEM for continents, and another for bathymetry, which made things much easier than all procedural displacement.
my work was mostly focused in clouds, but the yours is much more, well... procedural maybe?
I attached a pic of a volumetric gas planet. just very warped clouds, but its a similar technique than your continents i think.
another thing, is that you can also add icy poles to your planet easily, with large values of max/min altitude contraist to mask that zones.
like also auroras. dont doubt to send me a PM for any ask, and please, can you explain me again the general process of your planet?
Pd: the english isnt my lenguage, and the russian is translated much better to the spanish than to english, so russian its ok.