Rivian (RIVN 1.44%) has emerged as a strong candidate to move from young electric vehicle (EV) start-up to significant player. While the stock has trended lower as EV sales growth has slowed in the U.S., the company is still an intriguing long-term play you can scoop up on the cheap right now.But before you dive in, make sure you understand and can answer these three questions.1. Will Amazon hold Rivian back?At first glance, this question might seem odd. After all, Amazon's order for a total of 100,000 elec ...