As to the comma, the usual pace of speech in "blah blah, OK?" would suggest a comma, but this is really up to the style of the writer. I feel that OK As an imperative does not require a question mark. In general imperatives using questions do not (always) need them: "Miss Collins, will you close the window." "Miss Collins, close the window, OK." More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.