Disclaimer: You will get mostly anecdotes on these sites, you should not let any opinions on this site stop you from going for your goals. Following was our experience w/WashU>
You have a strong background for most elite universities including WashU. However, WashU only accepted 14% of the applicants. Like other elite Top 20 universities WashU could not accept all the great candidates that applied. Said differently whenever you apply to a Top 20 university there can be no guarantees. Your essays will matter and your “fit” for what they are looking can vary by school by year etc…
Regarding ED, if you apply ED and are offered admissions then they will also tell you if you are eligible for financial aid. If so, they are likely to meet whatever they deem to be your demonstrated need. For some students WashU will cover almost all costs - but again those are cases with clear demonstrated financial need. This does not mean that your family will think WashU’s assessment will be sufficient for them. But this will the case for any T20 university - based on the family’s financials the financial aid office of the university will determine your need and most of them will meet what ‘they’ deem to be your financial need.
Regarding Premiere scholarship, this is where WashU shines. We too felt ED would lesson the chances for the Premier scholarship. While I don’t have data to comment on that, my son applied ED and then later he applied for a Premier scholarship and it was awarded. It is a very generous 4 year scholarship that made WashU relatively inexpensive for us. However the Merit/Premier scholarship decisions are always after the ED process - ie Merit decisions are not until March even if you are accepted ED before then.
[[Background when my son was accepted ED, they said we were not eligible for financial aid because of income and assets etc… The financial aid office was very approachable, I asked them to reconsider, they asked for more info about our finances but they then came back politely with the same response - we were not eligible for financial aid because we do not have demonstrated need. By the way, this what we assumed would happen and families with similar financial circumstance to ours received no financial aid from the other T20 universities their children applied to]]
In the end, we feel fortunate that our son was accepted to his top choice and it seems like a great university. He really appreciated their midwest friendliness (we are from California) and the collaborative environment between the students at WashU seemed genuine. Btw, there is a WashU preview that you might want to attend.
Finally, demonstrated interest during the applications process matters at most top universities and it matters at WashU. You can show that in your essays and before applying you can find ways to reach out and get to know people there especially your regional admissions rep - perhaps they will visit your high school and you might visit the university etc… And again, attending the WashU preview could be a great way to show interest and learn a lot about the university. I recommend applying to WashU ED if you think it is a good fit for you.
Good Luck wherever you apply!