ok i have heard that when using short range melee weapons such as knives, crowbars, sticks, etc... the zombies dead blood can squirt out and touch your skin, if this happens ive heard that it can kill that part of your skin, is this true or not ?
Completely untrue, it can only affect you if it gets into an opening in you skin. Such as, your mouth, eyes,nose, ears possibly. An open cut would be really dangerous so i advise covering and treating all cuts and scrapes after every encounter.
As for the speed of infection. It depends on where you are bitten, if you are bitten somewhere that the virus gets into the bloodstream quicker the effects will take over a lot faster which is a good reason to cover your body as much as you can.....