I'll help you with the strap question. When you approach the bar with hand in oveverhand position, the strap can go on either side of the bar first. You can put it on the far side or the near side. To be correct it needs to be on the near side, aka your side. You will start by wrapping under the bar. The Incorrect way starts by wrapping over the bar.
One more way to foolfroof it is- approach the bar like your ready to deadlift. Turn your head and look at your right hand. This strap will go clockwise. Look at your left hand- this one will go counterclockwise.
If you take them in the correct direction, theres no way your grip will slip. If you're still having trouble, chalk the bar first where the strap is going go wrap. This creates an incredible amount of friction and really kindof makes it difficult to even get set right since the straps grab so hard, i think i would literally destroy something in my arms/ shoulders before this grip slipped.
If you still cant get this, let me know and i'll send you a video. Some people just cant understand that theres two different directions to wrap. They just cant "see" the other way. Lol.