Considering brief physical contact is sufficient for infection, if the Thing had opted not to transform (most obviously in the dog pen), it could have taken over everybody in the camp before anyone even realized there was a real and present danger. Of course, that would have been a quite short and relatively dull movie.
Well they did retrieve the corpse from the Norwegian camp, and Blair was analysing the blood sample. So perhaps the threat wasn't immediate, but Blair would have figured it out before things got that bad.
The reason the flamethrowers don't work doing the blood test scene is because the Palmer thing tampered with them. He was carrying a flamethrower thoughout the movie up until that point.
It's a possibility, but it's probably because Mac drops his flamethrower just before Palmer attacks.
Even supposing the Thing didn't create the flying saucer it landed in, it has the ability to create a new one, so there could be Things all over the universe.
Well, the common theory is that Things get smarter mostly by assimilating knowledge from their victims, and Word of God is that the 2011 film was originally supposed to prove that the Thing was picked up as a biological specimen by an entirely different alien race. So, only the Things descended from the first Thing to crash on Earth would know how to build spacecraft; it's equally as likely that "Thingworld" has been quarantined — or sterilized — to avoid just such an outbreak.
The implication I got was that this thing was a virus spreading across the entire universe.
Luckily, since the last thing arrived 100,000 years ago, they're probably dead, at least near earth.