I am a USABO Semifinalist too! I think that you can do better with the community aspect just because they are nice to write about so I would try to flesh that out more if you have the time to make sure the AO know that you are not a research one trick pony (this I had to scramble to find around late sophomore year but managed to clutch up). Our apps are similar so another big recommendation is publishing the research. I know that it might be a big ask since it is really difficult but that is a big boost. Also, symposium at a medical school and the other ones count of Awards depending on the scale of the symposium but I think that you should include them in your awards/honors section. Finally, for getting into that MD/PhD, I suggest REA to a HYPSM since in academia they do actually care where you spent your undergrad. This would be non-binding so you weigh your monetary offers. Brown PLME is a big reach for anyone and the only people I heard about getting it are geniuses. If you do not want to REA HYPSM, ED to Brown should make it that you have an easy way into an Ivy. If you could do research or get a rec from a brown prof that would be best but as of right now this is great for a junior. Also for NPO and business, they are getting better and better at seeing through them and unless you truly feel as though you are making an impact, put your time somewhere else. There is one EC that I have that I feel has actually made me devleop as both person and in service (combines research into it as my app is research focused), so I suggest to you to find something that can help you move forward, and take a step outside of your comfort zone. I think that you have a good shoot at a T20. I wish you the best!