I'm new to the forums (hi everyone!), but I can help you with this. :) I'll respond in order to your questions.
1. Your citation is correct but I would change the English. There are other options of course but one idea is this:
In his article, "Thank You, Dr. Miller, For Saving My Life," Neilson noted, “I'm happy to say Veterinary Medicine exceeded my expectations” (570).
2. Again your MLA citation is correct but I would change to something like this to address some issues in the intro sentence:
In his article, "Bankruptcies, Illness Linked," Anderson noted that
medical problems contributed to nearly two-thirds of all bankruptcies in the United States in 2007, according to a study in the American Journal of Medicine. Based on court-record reviews and interviews of more than 2,300 bankruptcy. . . . Most medical debtors were well educated, owned homes, and had middle-class occupations, the study found. (61)
Note that I intentionally lower cased the m in medical and changed to a period and 3 spaced dots for the ellipsis points.
3. Good job on your citation. I would change your text to this though:
Journalist Christie McLaren said, “The cost of the Ontario Drug Benefit Plan is rising 20 percent each year. Last year, Ontario spent $638-million on this plan - five times as much as a decade ago” (“Cost of Essential” 5).
Depending on the context, you might be able to use says, but if you do, still include the comma as I've done after said.
I'll respond to your questions about the references in a separate post in a moment.