Can we go and purchase tickets at gate? Or do we need to buy ahead of time??

I recommend buying tickets beforehand. When I went, the preticket line was about 20mins long while the regular ticket line was 4-6xs longer.

Yes, you can purchase tickets at the time of arrival.

Yes you can purchase tickets there. They are on sale from 7pm-10pm. https://www.nightterrorshauntedfarm.com/tickets/

You can purchase tickets there. If you don't mind possibly waiting in line for white. The lines can be extremely long