What are your neighbors using?
From what I can see Northern Tool is selling the Mighty Mule lower end systems, the Mighty Mule line is not known for long reliability
I guess nearly every manufacturer of gate operators has a system that will easily do what you desire. Like buying a compact tractor …who is going to service this once its installed?
Solar is no problem and be aware there still is a Federal Tax credit for a solar system (30% for 2019 reduced to 26% 2020) (check with your tax adviser)
If you go solar, you want a system that was Designed for solar applications not one that converted to Solar use as any electric operator can be made to run on solar,. These systems that are designed for solar will normally shut down all non essential power consumption devises after a specific time period (usually three to five minutes) thus reducing the size of solar panels and batteries required.
Battery size and type are pretty important features . Many models use a 7 ampH battery that really was never thought of to be used outside of an alarm panel which were to be mounted in an environment that was heated/cooled… they were cheap to purchase by the manufacturers so that is what they chose… I am pretty sure our bill of material cost was less than $5 for that type of battery. (seem to think it was more like in the $3.90 range for large purchases of 10,000 at a time)
“Free Exit” is commonly done using a exit probe which will allow any one to exit (unless probe is controlled by a time clock or switch to shut it off). Since you want a keypad entry, you can also use a keypad to exit (Mighty Mule/GTO also has a wireless exit probe that is battery powered, I think their expectation of battery life on the probe is five years)
There are as many bells and whistles that can be added to a system as there are breeds of dogs, with both adding new ones all the time