1) If you have your JHMCS on, and press the recce button, it will toggle it on and off. That is all I know for that button.
2) Sensor select Depress is used for IFF'ing targets on your RADAR, and other stuff on the SA page (I believe. I'm more of a Tomcat guys these days and have fallen behind on Hornet development).
3) Weapon Select Right will give you the 120's. Weapon select left is not used (couldn't tell you why. An AT or Pilot could probably answer that).
4) added it to keep button count the same from the Warthog. Also, works for other modules (Tomcat).