Bodybuilding form and powerlifting form are definitely different for bench.
Bodybuilders aim to maximize "Mind Muscle Connection" and perform the exercise specifically to target the chest (or tricep, if it's close grip bench) as much as possible, at the expense of how much weight they can move.
Powerlifters however will use as much muscle groups as possible to lift the biggest possible number, as well as reducing the range of motion as much as possible within the limits of the rules.
The arched back allows you to incorporate more power from the Lats (
http://en.wikipedia.org/wiki/Latissimus_dorsi_muscle) while the placement of the feet allow you to incorporate leg drive to further increase the number you can push
Nothing to be honest, haven't hit any walls so far so I haven't had a reason to try to train any weakspots, everything is still going up.
My lifting is honestly only squats, deadlifts, bench, overhead press, chinups and barbell/dumbbell rows, I like it simple
Yeah, I love bent over barbell rows and chinups/pullups too.
There will come a point when you WILL need to do assistance lifts though.
I don't need to do them as such, I know my deadlift, squat and bench will increase anyway since I'm still relatively new to lifting, but I do them anyway because they reduce the risk the risk of injury and I think it's better to get into the habit of doing them as early as possible rather than waiting.
Even core work is highly important, it's not just for bodybuilders. Doing direct core work can mean the difference between getting that lift up safely or getting a crippling injury once you start getting into the really big weights.
