Soooo I'm going to need help doing this since it's extremely detail oriented. Not sure if going at this from a full water or full land base is best. I'm still experimenting with using bo_subtract on different brushes to make the best one for getting water nicely spread and also for coastlines. I'm estimating around 400+csg for this all the way to 800. Thinking about using 0 temp earth to make it so no trees bug out while making it in editor and just changin it back to desired temp after
The problem after that though is what csgs do I use to create decent land. Basically creation of an artificial height map
csg does not look good as land. Although it'd be more of a hassle, starting with a full land base would probably better, especially since you're going for detail. (although i'm sure the inverse could also be argued )
To terraform the planet, you can try using moon craters to place the water where you want like i did on Ring Spoiler Yes it's kind of ugly but it's all what we've got and it works in terms of gameplay.