1. Absolute Yes.
2. Possible Yes. The definition is up to the immigration officer, but it would be much safe if you can prove the same or very similar job duties in your new position.
3. Yes or No. You're not required to keep job during 485 pending/AOS, but you need to have one (the original one, or a different one but with a same or similar occupational classification) handy when it reaches the time of approval.