I don't know the answer to either of your questions- The article indicates:
Every administration pushes to complete as much of its agenda as possible when a president’s term is coming to an end, seeking not just to secure its own legacy but also to tie the hands of any successor who tries to undo its work.
Coney Barrett, if appointed, can tip the scale- If Biden wins, he can add more justices and level it or stack it- I don't believe that's ever been accomplished, only attempted- It isn't against the Constitution because the Constitution doesn't contain any wording to reflect Supreme Court "size"-
Should Biden/Democrats win, stack the court, maintain the House and take back Congress, a Biden administration could have more leverage, hit the ground running and make Big Structural Changes that benefit not only the US-
In reality, I haven't a clue if a Biden win would benefit the UK because with tensions being what they are, haven't a clue what it will do to us as a country, should there be some sort of awful fallout-