Warm up question and overload question

Hey everyone. I’m going back to hitting strength 1 template as it’s time to get healthy and stop chasing numbers that don’t really matter if your out of shape. It’s been a while since I did a bbm template. I’ve always struggled with a few things, one of those things are warm ups. I use an app at times and had found a website that helped achieve warm ups but I’m not sure how accurate they are to bbms approach. For example I use to do a set of 5s with the empty bar. Than move up according the the app or website. It is usually went a set of 5s to the working set. Than I found the website and did 10 reps empty bar, a set of 5s, 3,2 than the working set.

last question is about the overload in strength one. I understand that you are suppose to use 20% of your 1rm in bands or chains. My question is do you subtract 20% off your working weight or add 20% to the working set? Example if your 1rm is 100lbs do you load the bar to 80lbs than add bands or chains to get the last 20lbs? Or do you add 100lbs to the bar and add chains or bands to 20% extra? I think it’s the first as I assume like in conjugate training you are moving weight faster but still adding a stressor to push gains.