I'm finally done with this process (into an English PhD program that fits me nicely), so it's nice to be giving advice to someone else for the first time.
Unless there's a compelling reason for you to take the GREs now, wait until the fall. As others have said, you're verbal score should be above 700. It's really just a vocabulary test, so the more time you spend with flashcards, the better you'll end up.
If you have plenty of time, take the subject test. It takes an enormous amount of studying to do well on that exam, so if you don't have the time, don't bother. I did very little studying for it, and guess what? Didn't exactly ace it, but it didn't hurt me too much in the end (good verbal scores made up for it, I think). Also keep in mind that many professors recognize the difficulty of the test and some even call it what it is--an expensive trivia test. It helps if you do well, but don't panic if you don't.
Apply broadly. You may love Vanderbilt, but you need to keep in mind that in some sense this whole process is a crapshoot. You may be an exceptional candidate, but it might not be in the cards for this admissions season. I'd recommend coming up with at least 10 schools. I applied to only five and one was an (MA), mostly because I kept psyching myself out or coming up with reasons not to apply or why the program wasn't a good fit. Guess how many admits I got? One. Luckily it was to a school that I liked, with good funding. It could have turned out quite differently.
You mentioned that you "believe" your writing sample is good. Why not try to get a little more input? If I had to do the process over, I'd definitely ask a professor to look over my sample. Page limits often mean you can't submit a complete undergraduate thesis (limits were often 20 or 25 pgs for my apps). Just having someone to talk to about what portions are the strongest would have been a great help for me.
Also, am I the only one who thinks that the GRE writing score doesn't (or shouldn't) matter? These programs usually end up with 25+ pages of writing from each applicant; why do they need ETS telling them how good an applicant's writing is?
Have fun with it all. Drink plenty of beer. It helps.