How many warm up?? ma no sure answer depends enough to get warm and depends on your strenght. i9 mean big difference in someone pressing 500lbs and someone pressing 200.
atleat 3 sets if you load is LOW im usually in the 4-5 zone I guess prior to the max attempt.
How much to jump again depends on the load used at the end. Dont waste your energy on Junk reps make a big Jump. At least 50 lbs Id say from last warm up to max. if your more advanced Id say jump a plate or so to your new pr (90) lbs
Try and keep warm up sets out of the 90% raneg of your attempted PR. save the energy for the PR you can always do another set AFTER the real work is done in the 90% raneg zone get todays goal as fast as you can.