It depends on the kind of data and where it will be coming from. Trigging your gate really only needs a signal to start moving, though a directional signal would be better ("Open" or "Close"). What is the source of that signal and far from from the gate will it originate?
If you're willing to press a button on the gate, it's a simple matter of sensing the ...
How do people generally get data onto the Arduino, I found a lot of conflicting information online.
There are various ways depending on what the data is and how you access it.
Does this thing have Wifi or Bluetooth??
Not unless you add WiFi or Bluetooth to it, no.
I have a raspberry pi spare, can I just use that, sending data from pins?
Yes, there ...