All good questions!

Distance from the nock: arrows are drag guided, meaning the fletching provides drag on the back of the arrow which keeps it flying straight. The fletching will work better the farther back it is. That being said, moving it and inch or so up or back will have no measurable performance impact. Most archers I know set their fletching as far back as they can without having it contact their face at full draw.

Offset or staggered fletching: People have tried this for a number of years with mixed results. All in all I don't see any real benefit to it.

There is no real negative impact to the arrow stopping rotation on impact. Any benefit that you would gain from an arrow that did not spin in flight would be negated by the fact that it would probably not be accurate. No arrow is built perfectly nor is it areodynamicly perfect. If the arrow did not spin, any small misalignment of the broadhead or vanes would cause the force due to air pressure to be applied to that side of the arrow during the entire flight, causing it to veer off course. By spinning, any misalignments or inconsistencies are applied at all angles during the arrow flight, in essence averaging out any inconsistencies. As for it's effect on penetration, theoretically there is some small impact on overall penetration, however it is probably so small that it is not measurable.