Is skipping necessary? can footwork/conditioning be improved sufficiently without?
Necessary, no, but it's probably as close to necessary as you can get without being essential. It will improve your footwork, your coordination between your hands and feet together, and your rhythm. It is a fantastic exercise that everyone should do, but essential, no not quite in my view.
Does punching the heavy bag bareknuckle strength the hands? if so, how many rounds a week should i do?
It will help build calloused skin on top of the knuckles, and kill the nerves there. Hitting hard without gloves is a skill in itself, and hitting the bag without gloves will teach you proper wrist alignment so you can hit bareknuckle an reduce your risk of injury. Sento is the one to get detailed information from on this, as he will know much more than me. My own suspicion is that too much of this is likely to lead to problems in the future, like arthritis, but I may just be trotting out old wives tales.
i hear pads are overrated. that ali, duran etc. never used them. thoughts?
I think they become much less important once you reach a high degree of ability. Once you have perfect technique ingrained from years of work with a trainer, shadow boxing is more effective, as you can get in a lot more rounds but put less stress on your joints. While you still make fundamental errors, working with a coach on the pads is highly valuable. As with many things, the training hierarchy changes as you progress, and depending on the type of fighter you are. For example, I can prepare for competition more effectively by doing fairly limited sparring, but at a very high intensity, with a much greater emphasis on shadow boxing under coach supervision. Other fighters may need more time with particular types of sparring, or to achieve certain milestones in their sparring preparation.
how can you strength punch resistance (chin)? any theorys other than genetics? ive heard neck training helps brace the impact?
I don't know that there are any studies on this, or that there is anything conclusive out there. That said, I swear by regular high rep neck work and bridging work, and have always felt it made me more punch resistant. Whether it is psychosomatic or not doesn't really matter. If you arrive at competition optimally prepared from head to toe, you will handle everything better when it comes your way. Ultimately, if you're going to get sparked out, it's goin to be from a good punch you haven't seen coming. I can't see anything saving you at that point, however a solid base of neck work may determine how fatigued you are when the big punch lands, how much cumulative damage the punches before have done. That may play a part in how badly hurt or disorientated you are.