The first thing to do is find a gate is to figure out how much voltage & amperage the motor will draw when opening the gate under a load. Then figure out the best / easiest way to deliver about 50% more power than that. A gate will be harder to open in the winter if you get snow. The motor will draw more power to open it. Also if you go solar, use a bigger battery then needed because of the loss of power when it’s cold.

I would have to imagine there are lots of powered gates made so it should not be too hard to find a 12-volt one. Don’t forget a weatherproof housing for the electronics.