You will need Fallout 4 installed on your PC in order to load the game data; the Creation Kit is only an application, it doesn't come with any game data. As for what kind of PC you'll need to run it... I used to play Skyrim on a laptop that was never meant to run Skyrim. After reducing all of the graphics options I could (save for texture size), running at the lowest resolution, and using a disgusting amount of performance-enhancing drugs mods, I managed to get Skyrim at a "playable" 15ish FPS.
But with that laptop, I managed to use the editor mostly just fine. I tried making a dungeon, and the only snag I hit was when I tried to add lighting to it - that might have been a bug within the editor itself though. I never tried anything intensive, like landscape editing, though. But http://www.nexusmods.com/skyrim/mods/34184/? was made on that crummy laptop, and all I did for that one was adjust NPC templates, leveled lists, and inventories. I never had any major problems with performance.
I wonder if we can ask what the standard PC build at Bethesda Game Studios is. I bet if someone modded on the same setup Bethesda uses in-studio, the Creation Kit would run a lot more smoothly for them. It's like that with Pro Tools; if you're trying to run Pro Tools on a Windows rig, you need a very specific build for it not to choke up and cause problems. (but honestly, even on Apple, Pro Tools may as well have been developed by Bethesda for how buggy it is)