I think if you have margin account, you will be able to use leverage, that is what margin account means.
Not for Options. TDA charges $0.65 per contract per leg. See https://www.tdameritrade.com/pricing.page
Capped at $30 but you have to pay $55 to use their platform on top of that! I am now comparing Tradier to TW to see which one is cheaper. They both root orders to APEX anyways....