Would taking a Teacher Assistant period senior year hinder my application to T10s, 20s, etc?

I think you shouldn’t obsess over rankings. “T10” “T20” are arbitrary pet schools rearranged by US News every year. You might as well be using the supermarket tabloids to compile your list. Instead, focus on the job skills you want to obtain in college and find an affordable school that can get you there. You’re the one choosing the school to gain those skills, not them.