Not an expert by any means but I thought I would share my experience moving from SS to 5/3/1. I'm 52. I finished at 265 Squat, 255 DL, 190 BP, and 125 OHP. I cut it short due to back pain and plan to go back to LP after the Summer.
I've enjoyed the move. I feel like I recover better doing just one main lift a day and not doing three/four main lifts three/two times per week.
I found that my 5 Rep number was a good place to start my training maxes. I do AMRAP on the final sets without issue. Some days I "work up" by adding FSL (using the weight of your first set after the AMRAP for another AMRAP set).
I'm currently doing Triumvirate but do not think the accessory template you choose is that important. Focus on the main lifts and particularly the AMRAP set. I like the ability to change accessory work after a cycle or three to keep it interesting.