Question: Was any member of the team aware that they were infected by the creature, or did they not know they were until they began changing?
Answer: The thing was most likely trying to act like the deceased person it assimilated in order to fit in and avoid potential extermination.
Question: Someone proposes an initial blood serum test (before Macready's heat sensitivity test), but the crew find the blood sabotaged before they can get to it. How could "The Thing" have gotten to the blood so fast, and more importantly, Garry and the Doc are the only ones said to have access to the blood. BOTH are proved by the Mac's test to be "Thing-free" - the Doc's blood is tested even though he is dead; Garry is the last man tested. How can this be?
Answer: The Thing is a shape shifter. It doesn't just take the form of what it assimilates, it can change its shape (eg. dog and head spider). It could easily form a thin tentacle to open a door from the inside. It's also shown to have the sheer strength to bust out.
Question: Was the huge monster McReady encounters, and subsequently blows up, the actual "default" form of the Thing? After all, the correspondent DVD chapter is titled "The Real Thing". Yes, they do say that the Thing could've imitated millions of different lifeforms, but it must've had a form to begin with.
Answer: In the book, it was vaguely humanoid with blue rubbery skin, a head of writhing tentacles, and 3 glowing red eyes. There is a picture of it in Barlowe's Guide to Extraterrestrials by Wayne Barlowe.
Question: So what happen to the two guys at the end of the movie? Are there any stories about them in the PC game or an alternate ending or something like that?
Answer: No one knows what happened. They had no transport and couldn't make radio contact, so very likely they froze to death. If one or both are Things, than they just went dormant until rescue shows up. There is nothing in the game or on the DVD that answers this for sure. BTW It's very hotly debated amongst Thing fans, that Childs is a thing because you cannot see his breath in the cold. (It's very difficult to tell if you can or not because of the scene's lighting).