If you enjoy teaching/mentoring (which it seems like you do), I'd recommend volunteering at a local high school or community college and teaching some classes or tutoring students. You get to meet a wide range of students and get the chance to make their learning environment exciting and interesting! Teach whatever interests you - could be music, art, math, etc.
For top-tier MD programs, you want to aim for a 518+ to be on the safer side so that they aren't really reaches. For MD/PHD programs at said top-tier MD programs, you should probably aim for a 521+.
You're also going to need a lot more than 25 hours clinical experience.