You are fine if you are behind a router on a local network at home and don't have SMB port exposed to the public internet. And assuming all other clients on your network aren't infected.
No! All it takes is a single byte to be patched and the "killswitch" can be disabled. There are almost certainly other variants already in circulation.
Yep, tried doing that. But unfortunately I could get it to install. Keep getting "This update is not applicable to your computer" even though I'm doing everything right.