I put blocks under both tires. I don't know what is "correct" but I think it is silly to torque the axles. Just back on blocks on the low side and get it "close"
After the side to side is level simply level it front to back with the tongue jack. You are done!
Put the stabilizing jacks down to help stiffen things up. No, it won't be perfect. Your trailer comes with stabilizers at each corner. Some add additional ones but that sounds like a lot of work to me. The heavier the trailer the more stable is seems.
Your questions 5 and 6 show that you are over thinking this. Once it is level you might have one side sitting on the springs more than the other. But once you snug up your stabilizers the springs are more or less removed from the discussion.
Hey, it is a trailer, not an aircraft carrier. It will have some movement even under the best of circumstances.
