You can, all you need to do is highlight the docking port on the other ship and double click on it. It can get a little hard getting the right part highlighted when you are a fair distance away, but you can still do it.
It would have to be a massively strong magnetic field - many times higher than Earths. The gas giants simply put out way to much electromagnetic radiation in the direct area around them. Bit of useless trivia: If they had not done the Pioneer missions prior to sending Voyager it would have been fried by the time it reached Jupiter and we would have had no further contact with it. Pioneer found there was way more radiation than they had expected, and Voyager was a more complicated probe that would have been killed had it not been fitted with the extra shielding added after the pioneer results.
You cant have any direction key pressed when you hit R, or else the RCS wont kick in. That has caught me out a few times when the kerbal has been spinning out of control.
I have had that multiple times. The funnier ones are when you have a booster that is sitting a good 50-100m away from the ship. It will still fire and give you thrust, but it usually blows up on stage separation. The trigger i have found is when you have multiple types of symmetry that somehow get confused.