Post Scriptum welcome to the QR forum.
It is almost always possible to select other seats on any flight unless it is sold out.
A word of warning: bassinet seats (or rather the front row of most cabins) are always blocked. So were you to try to change seats you would not be able to reserve a bassinet seat yourself. Of course you could contact reservations again and get them to move you but even then you cannot be sure that you can get a bassinet seat.
Your other questions I will leave to those who have used bassinet seats previously.