You have installed on the wrong side. Determine if you want your gate to open in or out. Facing the gate on the side that pushes away from you attach the spring on the hinge side at a near vertical position. That way when you open the gate - push away from you - the spring will return the gate to a closed position. Adjust the tension to how strong a "close" you want.
With the spring attached to desired opening side of gate, you still can swing the gate in either direction. The spring closing action will only apply to the opening side.
Yes you sure can, but clamp it to the metal posts or drill through it using bolts with washer/nut on back side so it won't pull the screws out. Has a lot of tension for sure. I clamped mine on posts btw.. I also had this spring on my old wooden gate over a decade without one issue.
Use 2 sets of vice grips and tighten the the actual spring not the "top" or Hex Head of the spring (as the instructions state). You do this by using one vice grip to tighten the spring, then use the 2nd vice grip to hold the spring in place allowing you to then take the first set of vice grips off and re-place it for the next tightening turn. It also helps to have a 2nd person intermittently use a crescent wrench to hold the hex head in place as you continue to tighten the actual spring with your vice grips. If you use this method you are half way home. Here is another big problem. The "stop" provided which is placed between the mounting bracket and the flat side of the hex head IS TO TALL (by about a centimeter or 2). It does not fit because there is not enough space when your mounting screws of choice are in place. I had to fabricate my own "stop" so it would work. If you can do all of this then you will be able to complete this job.
Yes, it is a very strong spring with a lot of closing torque.
It's about 3/4 inches
I find the longer 14inch spring provides better closure when tension is reduced.