I'd try to stick with one of your volunteering gigs for longer to show commitment, as having a longitudinal experience would add to your application, but otherwise your ECs seem decent. You could also increase leadership, but it seems like you have at least 1 activity there, so that's by no means necessary. In general, make sure that you can talk/write passionately about your ECs - being able to convey them will be as important as what you've actually done when it comes time to apply.
I wouldn't worry about being a TA - not necessary unless it interests you - and as said above, no need for further shadowing.