Auto Step and Speed Indicator

I am completely frustrated because I am making a Super-Hero mod and while I'm doing the Flash I am having a lot of trouble, I wanted to make so if I hold the letter F on the keyboard the speed would increase, all I could do was pressing F toggling the speed and I wanted to add step assist when I'm in super speed, I can code, I also want a speed indicator, when I am wearing Flash suit the indicator appears, the speed limit would be 70 and if I keep holding F the number will increase from 0 until I release the key