Glad to help and I provide a number of training tips in my Inside College Volleyball book!
For Armswing, do the wall hitting drill. So much of hitting hard is making consistent contact with your hand upon the ball. Stand about 7-10 feet from a brick/hard wall, hit the ball into the ground, so it bounces up into the wall, then rebounds off the wall and up high enough for you to immediately attack it back down again. The goal is to be able to continuously hit the ball down and off the wall, and it sounds easier than it is.
Back in the day, this was how hitters warmed up their arms and practiced their armswing's. When you do this drill, it is easier to 'pre-load' arms (off arm up and forward, attack arm up and back), to keep the ball bouncing continuously.
While you don't want your arm bent when attacking, I don't know if fully straight is optimum. I usually see just a hint of bending in the arm upon attack, which I think gives a little more control and opportunity to change attack angle at the last minute. Again, the wall attack drill will help with this.
When you say 'pull back your arm to hit', this is called loading your attack. The motion is the same as if you were playing catch with a baseball. When you play catch with proper technique, your off arm moves forward and up, along with your left foot stepping forward, while your right arm/elbow lifts up and back behind your head. The pre-throw/attack position looks a little like those Greco-Roman statues of spear throwers. Then, the throw/attack motion is just pulling your off arm down into your body, rotating your hips and throwing the ball.
For your approach, after you know you have the correct footwork (if you are right handed, your left foot should be your last step and should be in front of your right foot), I suggest the high bounce drill. Use a partner or the wall (if using a wall, be a good 30 feet from it). Toss the ball super, super and I mean super high, into the air and so it lands about about 10 feet in front of you. As the ball bounces up off the ground, slowly start your approach, and time it so you can jump and attack the ball as it nears its apex.
This is a tough drill to do, and took my collegiate players a bit to get it, even though I swiped it from a 12 year olds practice I saw down Brazil! As simple as this drill may seem, it forces you to hit the ball with timing.
A challenge with our great sport is the ability to practice skills individually. These two drill suggestions allow for quality repetitions and you don't need a partner, much less a net.