If you just select the whole thing and start going to town with your tools, you'll soon find the bottom side of your landscape will end up being accidentally edited a bit, which we don't want.
Remember to use the select tool at the displacement options screen to only pick out the top 6 surface pieces. This prefab will serve as your landscape. I would stick with the 3 sizes above smallest. The smallest is pretty, well, small, and is really only good for moons you're just adding in for detail. Generally, unless you're only going to have about 3 or 4 planets on the map, or want to make a really realistic giant planet, don't use the largest size.
These are just some better instructions. ) You'll still need the sky-box and planet prefabs from the dev kit though.
This is a more advanced how-to for Shanjaq's SB dev kit that I hope is more user friendly to those Hammer newbies out there. All credit to whoever wrote this! You can download the origional document, along with all files mentioned
