Try dealing with turbo lag. You’d be perfectly fine in second. Even if you must be in first you’ll learn the most basic principle of throttle control.
Trust the people that have done both and started with autocross first. You learn a lot about balance, momentum, throttle control, braking control, etc in an autocross. It’ll come in handy a bit when you’re getting lapped by a 115hp E30. Those cars are dogs in every gear at every rpm, but they still manage to do work on track.