I think I am almost done my revisions! 15-hour work days do pay off. And now, time to prepare for classes...
Question: Is a seven-page letter to the editor that addresses the reviewers' comments (1) over the top, (2) too short, or (3) about right?
Congratulations. There is no right answer to your question, however, only "it depends". Sorry.
Science_expat is right, stratejem, it depends. Your letter should be long enough to respond to each comment made by the reviewers, and no longer. Therefore, the length of your letter depends on (a) how many comments there were, (2) what your response to each comment is. If you did exactly what was suggested in a comment, then your response really doesn't need to be much longer than, "Done." But if your revision isn't exactly what was suggested (or you decided not to revise in a particular instance, perhaps because you disagreed with the comment), then you need to explain why. Your explanation should be brief, but persuasive enough to show that you didn't just blow the comment off.
Also, does your seven-page letter include the actual comments? I structure my R&R letters comment by comment; the comment is in one typeface and my response is in another, to make the two visually different and easy to identify. This practice, of course, makes the letters longer--but more helpful to the editor and reviewers, I think.
I hope this helps.