Can you buy the parking ticket right when you enter the park or do you have to do it online?

You pay for parking before you park unless you have an upgraded season pass

Yes

We bought preferred parking at the gate. Buying online has processing fee so unless you are buying tickets with it, it is not worth buying online.

Yes, you can pay for regular parking at the gate, $25. Preferred parking is the one you have to reserve ahead of time, online.

Yes... But if you buy a season pass or membership.. Parking is free. Otherwise it's 25 at the gate