The windshields of modern day cars are made of laminated glass and cannot break the way it is shown in the beginning of the episode.
Mary Ann says that based on the government's previous experience with the rift, Theodore can't take anything new back with him. But Kaminski never said anything like that, and the implication is that the government never tried. All Kaminski said is that the time traveler has to take everything back with him that he brought: that doesn't exclude new items.
Mary Ann and Theodore both speculate that the rift--and whoever is controlling it--deliberately sent Theodore through time to accomplish something. Which means in all the other incidents that Kaminski mentions and Bowman hints at it, not once did a traveler succeed at whatever they were transported through time to do. That seems like absurdly bad planning, since thousands die in the various catastrophes... and not a single traveler ever succeeds until Theodore does.