This order seems a bit strange. Why are Midd and CMC down below Washington and Lee, Smith, Vassar, Grinnell, and Wellesley?
HMC’s selectivity is hidden behind an acceptance rate which is also determined by having a smaller pool of stronger students who are interested in an engineering LAC. However, the rest of the colleges have more or less similar applicant pools, so their acceptance rates are a decent reflection of selectivity. So Smith is accepting 32%, Vassar is accepting 22%, and you put both as more selective than than CMC, which is accepting 10%, and Middlebury with 17%.
U.S. News considers only student characteristics (as estimated by HS class standing and standardized scoring profiles) for its selectivity ranks. For example, Smith (#12) gets a boost from enrolling 75% of its students from the top 10% of their HS classes (to the extent that data are available for this figure) compared to Wesleyan (#19), which enrolls 67% from the top 10%. Because of this approach, some of the placements will appear counter-intuitive to those who (with justification) would include acceptance rates in the formula as well. For reference, the ranks as posted up-topic were taken directly from the current print edition of USN’s college guide.
At least in this admission cycle, it was open to everyone, virtually of course. My D applied, didn’t get in, then got into POP, and after it, nothing compared to Pomona anymore… Good luck
To get back to your original question, I do not see any problem with applying ED to Williams as long as (i) You are sure it is your top choice (this seems solid based on what you said); (ii) You are pretty sure that you can afford it (either you are fine being full pay, or you have run the NPC and you and your parents are fine with the results); and (iii) You have also figured out and applied to at least two solid safeties.
So, I think that you need to check the full price at Williams, plan for 5% per year inflation, and see if your parents are fine with this. If not, then you need to run the NPC. You will need help from your parents to run the NPC. If your parents own a small business, farm, or rental property or of your parents are divorced then the NPCs will be way too optimistic.
Then you need to find two solid safeties that you know you will get accepted to, you know you can afford, and that you would be happy attending. I have not seen any safety mentioned so far on this thread.
︎1. Pomona