I'm also loving the game.
There are a few bugs, the latest patch however has pretty much fixed everything that was wrong (Although as I write this, the game just crashed on me). Tripwire is doing a great job on fixing issues and supporting the game. Single player is pretty much multiplayer but with bots, but it's fun non the less. This is also a PC only game, Made for PC by PC players and developers, No console ports here.
As for the SDK, it's coming soon. Tripwire says that their priority at the moment is fixes, patches and to get the game perfect for everyone. I was able to find out that it may require 64 bit windows, as the amount of memory required to "build" aka compile maps uses is at least 6GB even on low detail with a small to medium sized map.
Tripwire staff member johnein posted this on the official forums...
I built Pavlov's House on Preview (lowest quality setting, with Production being the highest) and this is what the memory usage was. I'd say you might be able to skate by with 6GB on a low detail, small/medium sized map.
So it looks like the SDK is going to need, but not necessarily require at least 6GB of RAM to build maps, I guess you could get away with less but if you want to actually play the map in the next ten years it going to be a struggle.
I'll let you guys know when I have some more information.
On a side note, Anyone else remember Pavlov's house from CoD1?. I loved that map and it's just as good in this game.