Quiz Results slide 'Review area' - I want to bypass built in text box and create my own?

You are definitely on the right track.  Here are a few suggestions:

• If you are not going to use the current Review Area box, make it as small as you can and move it down into one of the corners of the slide.  Don't remove it completely because that sometimes causes issues with functionality and reporting.
• If you make the Retake Quiz button on the Quiz Results slide large enough to cover the Continue button, this will prevent the student from continuing past the Quiz Results slide by accident and then having to relaunch the lesson just to make another attempt on the quiz.
• The way I prefer to show the Pass/Fail feedback on the Quiz Results slide is to have a single Smart Shape placed there just below the Retake Quiz button.  I have four states on that Shape.  One that is blank, one for Pass, one for Failed but still have more attempts allowed, and one for when the user has failed with no more attempts. 
• I use a Conditional Action to change to one of these states depending on the situation at the time the student reaches the Quiz Results slide.  In my case the Conditional Action is fairly complex because I am also tracking variables that count the number of attempts the user still has left.  But you can cut your teeth on Conditional Actions with a much simpler setup that just consists of maybe two states for the Smart Shape and swap between them according to the Pass Fail result.